chore: check if record exists on delete keys mutation

[jyeshe]

Protection to avoid:

2023-05-11 14:37:19.566 [info] Application ae_mdw exited: bad return value: {{AeMdw.Application, :start_phase, [:dedup_accounts, :normal, []]}, {:EXIT, {%RuntimeError{message: "Txn delete on missing key: Elixir.AeMdw.Db.Model.AsyncTask, {1682903942917498353, :store_acc_balance}"}, [{AeMdw.Database, :delete, 3, [file: 'lib/ae_mdw/database.ex', line: 157]}, {AeMdw.Db.TxnDbStore, :delete, 3, [file: 'lib/ae_mdw/db/txn_db_store.ex', line: 42]}, {AeMdw.Db.State, :delete, 3, [file: 'lib/ae_mdw/db/state.ex', line: 152]}, {Enum, :"-reduce/3-lists^foldl/2-0-", 3, [file: 'lib/enum.ex', line: 2396]}, {:maps, :fold_1, 3, [file: 'maps.erl', line: 233]}, {Enum, :"-reduce/3-lists^foldl/2-0-", 3, [file: 'lib/enum.ex', line: 2396]}, {AeMdw.Db.TxnDbStore, :transaction, 1, [file: 'lib/ae_mdw/db/txn_db_store.ex', line: 23]}, {AeMdw.Db.State, :commit, 3, [file: 'lib/ae_mdw/db/state.ex', line: 56]}]}}}