Remove unneeded trait bounds (#8765)

Before we required these trait bounds because of some bug in rustc, but
now as this bug is fixed they can be removed.

substrate/test-utils/runtime/client/src/block_builder_ext.rs

@@ -20,7 +20,6 @@
 use sp_api::{ApiExt, ProvideRuntimeApi};
 use sp_core::ChangesTrieConfiguration;
 use sc_client_api::backend;
-use sp_runtime::traits::HashFor;
 
 use sc_block_builder::BlockBuilderApi;
 
@@ -49,9 +48,6 @@ impl<'a, A, B> BlockBuilderExt for sc_block_builder::BlockBuilder<'a, substrate_
 			StateBackend = backend::StateBackendFor<B, substrate_test_runtime::Block>
 		>,
 	B: backend::Backend<substrate_test_runtime::Block>,
-	// Rust bug: https://github.com/rust-lang/rust/issues/24159
-	backend::StateBackendFor<B, substrate_test_runtime::Block>:
-		sp_api::StateBackend<HashFor<substrate_test_runtime::Block>>,
 {
 	fn push_transfer(&mut self, transfer: substrate_test_runtime::Transfer) -> Result<(), sp_blockchain::Error> {
 		self.push(transfer.into_signed_tx())