chore: remove mutex (#4617)

Description
---
Removes mutex added in #4613 

Motivation and Context
---
While the race condition is definitely possible in code, all code from the OMS runs synchronously, as shown by the fact that almost all functions have `&mut self` and rust blocks mut borrow across threads. This means that there is no race condition possible as this is all called synchronously. 

How Has This Been Tested?
---

base_layer/wallet/src/output_manager_service/service.rs

@@ -1134,56 +1134,9 @@ where
             )?)
         }
 
-        // let mut change_keys = None;
-        //
-        // let fee = Fee::calculate(fee_per_gram, 1, inputs.len(), 1);
-        // let change_value = total.saturating_sub(fee);
-        // if change_value > 0.into() {
-        //     let (spending_key, script_private_key) = self
-        //         .resources
-        //         .master_key_manager
-        //         .get_next_spend_and_script_key()
-        //         .await?;
-        //     change_keys = Some((spending_key.clone(), script_private_key.clone()));
-        //     builder.with_change_secret(spending_key);
-        //     builder.with_rewindable_outputs(&self.resources.rewind_data.clone());
-        //     builder.with_change_script(
-        //         script!(Nop),
-        //         inputs!(PublicKey::from_secret_key(&script_private_key)),
-        //         script_private_key,
-        //     );
-        // }
-
         let mut stp = builder
             .build(&self.resources.factories, None, u64::MAX)
             .map_err(|e| OutputManagerError::BuildError(e.message))?;
-        // if let Some((spending_key, script_private_key)) = change_keys {
-        //     // let change_script_offset_public_key = stp.get_change_sender_offset_public_key()?.ok_or_else(|| {
-        //     //     OutputManagerError::BuildError(
-        //     //         "There should be a change script offset public key available".to_string(),
-        //     //     )
-        //     // })?;
-        //
-        //     let sender_offset_private_key = PrivateKey::random(&mut OsRng);
-        //     let sender_offset_public_key = PublicKey::from_secret_key(&sender_offset_private_key);
-        //
-        //     let public_offset_commitment_private_key = PrivateKey::random(&mut OsRng);
-        //     let public_offset_commitment_pub_key = PublicKey::from_secret_key(&public_offset_commitment_private_key);
-        //
-        //     let mut output_builder = UnblindedOutputBuilder::new(stp.get_change_amount()?, spending_key)
-        //         .with_script(script!(Nop))
-        //         .with_input_data(inputs!(PublicKey::from_secret_key(&script_private_key)))
-        //         .with_script_private_key(script_private_key);
-        //
-        //     output_builder.sign_as_receiver(sender_offset_public_key, public_offset_commitment_pub_key)?;
-        //     output_builder.sign_as_sender(&sender_offset_private_key)?;
-        //
-
-        //     let change_output =
-        //         DbUnblindedOutput::from_unblinded_output(output_builder.try_build()?, &self.resources.factories)?;
-        //
-        //     db_outputs.push(change_output);
-        // }
 
         if let Some(unblinded_output) = stp.get_change_unblinded_output()? {
             db_outputs.push(DbUnblindedOutput::rewindable_from_unblinded_output(

base_layer/wallet/src/output_manager_service/storage/sqlite_db/mod.rs

@@ -22,7 +22,7 @@
 
 use std::{
     convert::{TryFrom, TryInto},
-    sync::{Arc, Mutex, RwLock},
+    sync::{Arc, RwLock},
 };
 
 use chacha20poly1305::XChaCha20Poly1305;
@@ -68,15 +68,13 @@ const LOG_TARGET: &str = "wallet::output_manager_service::database::wallet";
 pub struct OutputManagerSqliteDatabase {
     database_connection: WalletDbConnection,
     cipher: Arc<RwLock<Option<XChaCha20Poly1305>>>,
-    encumber_lock: Arc<Mutex<()>>,
 }
 
 impl OutputManagerSqliteDatabase {
     pub fn new(database_connection: WalletDbConnection, cipher: Option<XChaCha20Poly1305>) -> Self {
         Self {
             database_connection,
             cipher: Arc::new(RwLock::new(cipher)),
-            encumber_lock: Arc::new(Mutex::new(())),
         }
     }
 
@@ -663,12 +661,6 @@ impl OutputManagerBackend for OutputManagerSqliteDatabase {
         let start = Instant::now();
         let conn = self.database_connection.get_pooled_connection()?;
         let acquire_lock = start.elapsed();
-        // We need to ensure that this whole encumber operation happens inside of a mutex to ensure thread safety as the
-        // transaction first check checks if it can encumber then encumbers them.
-        let _guard = self
-            .encumber_lock
-            .lock()
-            .map_err(|e| OutputManagerStorageError::UnexpectedResult(format!("Encumber lock poisoned: {}", e)))?;
 
         let mut outputs_to_be_spent = Vec::with_capacity(outputs_to_send.len());
 
@@ -723,12 +715,6 @@ impl OutputManagerBackend for OutputManagerSqliteDatabase {
         let conn = self.database_connection.get_pooled_connection()?;
         let acquire_lock = start.elapsed();
 
-        // We need to ensure that this whole encumber operation happens inside of a mutex to ensure thread safety as the
-        // transaction first check checks if it can encumber then encumbers them.
-        let _guard = self
-            .encumber_lock
-            .lock()
-            .map_err(|e| OutputManagerStorageError::UnexpectedResult(format!("Encumber lock poisoned: {}", e)))?;
         let outputs_to_be_received =
             OutputSql::find_by_tx_id_and_status(tx_id, OutputStatus::ShortTermEncumberedToBeReceived, &conn)?;
         for o in &outputs_to_be_received {