Simplify tracing_subscriber initialization in the examples (#1524)

The default features of `tracing_subscriber` already initialize `tracing` with
`tracing_log` and the env filter when `tracing_subscriber::fmt::init()` is used.

examples/e06_sample_bot_structure/src/main.rs

@@ -22,7 +22,6 @@ use serenity::{
     prelude::*,
 };
 use tracing::{error, info};
-use tracing_subscriber::{EnvFilter, FmtSubscriber};
 
 pub struct ShardManagerContainer;
 
@@ -56,11 +55,8 @@ async fn main() {
     // Initialize the logger to use environment variables.
     //
     // In this case, a good default is setting the environment variable
-    // `RUST_LOG` to debug`.
-    let subscriber =
-        FmtSubscriber::builder().with_env_filter(EnvFilter::from_default_env()).finish();
-
-    tracing::subscriber::set_global_default(subscriber).expect("Failed to start the logger");
+    // `RUST_LOG` to `debug`.
+    tracing_subscriber::fmt::init();
 
     let token = env::var("DISCORD_TOKEN").expect("Expected a token in the environment");
 

examples/e15_simple_dashboard/Cargo.toml

@@ -10,7 +10,6 @@ rillrate = "0.39"
 
 tracing = "0.1"
 tracing-subscriber = "0.2"
-tracing-log = "0.1"
 
 webbrowser = "0.5"
 

examples/e15_simple_dashboard/src/main.rs

@@ -335,15 +335,11 @@ async fn main() -> Result<(), Box<dyn Error + Send + Sync>> {
         "info,e15_simple_dashboard=trace,meio=warn,rate_core=warn,rill_engine=warn",
     );
 
-    // Increase compatibility with tracing and the log crate macros used by RillRate.
-    // Some weird things get logged without this if you use tracing.
-    tracing_log::LogTracer::init()?;
-    // Since we use tracing_log, we need to use a different way of subscribing to tracing events
-    // than shown in example 7.
-    let subscriber = tracing_subscriber::FmtSubscriber::builder()
-        .with_env_filter(tracing_subscriber::EnvFilter::from_default_env())
-        .finish();
-    tracing::subscriber::set_global_default(subscriber)?;
+    // Initialize the logger to use environment variables.
+    //
+    // In this case, a good default is setting the environment variable
+    // `RUST_LOG` to `debug`, but for production, use the variable defined above.
+    tracing_subscriber::fmt::init();
 
     // Start a server on `http://0.0.0.0:6361/`
     // Currently the port is not configurable, but it will be soon enough; thankfully it's not a