deps: remove polkadot-sdk umbrella crate (#1926)

* deps: get rid of polkadot-sdk umbrella crate

* fix nits

* Update subxt/src/backend/mod.rs

* Update subxt/src/events/events_client.rs

* Update metadata/src/utils/validation.rs

* cargo clippy fix

* fix ui tests

testing/integration-tests/src/full_client/storage/mod.rs

@@ -3,7 +3,6 @@
 // see LICENSE for license details.
 
 use crate::{node_runtime, subxt_test, test_context, utils::wait_for_blocks};
-use polkadot_sdk::sp_core;
 
 #[cfg(fullclient)]
 use subxt::utils::AccountId32;