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/client/cli/src/runner.rs

@@ -345,7 +345,6 @@ mod tests {
 				transaction_pool: Default::default(),
 				network: NetworkConfiguration::new_memory(),
 				keystore: sc_service::config::KeystoreConfig::InMemory,
-				keystore_remote: None,
 				database: sc_client_db::DatabaseSource::ParityDb { path: PathBuf::from("db") },
 				trie_cache_maximum_size: None,
 				state_pruning: None,