Keystore overhaul (iter 2) (#13634)

* Remove bloat about remote keystore

* Update docs and remove unused 'KeystoreRef' trait

* Use wherever possible, MemoryKeystore for testing

* Remove unrequired fully qualified method syntax for Keystore

substrate/utils/frame/try-runtime/cli/src/lib.rs

@@ -816,9 +816,10 @@ pub(crate) fn full_extensions() -> Extensions {
 	extensions.register(TaskExecutorExt::new(TaskExecutor::new()));
 	let (offchain, _offchain_state) = TestOffchainExt::new();
 	let (pool, _pool_state) = TestTransactionPoolExt::new();
+	let keystore = MemoryKeystore::new();
 	extensions.register(OffchainDbExt::new(offchain.clone()));
 	extensions.register(OffchainWorkerExt::new(offchain));
-	extensions.register(KeystoreExt(std::sync::Arc::new(MemoryKeystore::new())));
+	extensions.register(KeystoreExt::new(keystore));
 	extensions.register(TransactionPoolExt::new(pool));
 
 	extensions