Relax Send/Sync/Clone requirements for Pair (#14647)

* Relax Send/Sync requirements for not instanced generic Pair

* Remove leftover

* Apply review suggestion

Co-authored-by: Sebastian Kunert <skunert49@gmail.com>

* Further cleanup

* Trigger CI

---------

Co-authored-by: Sebastian Kunert <skunert49@gmail.com>

substrate/client/consensus/common/src/import_queue.rs

@@ -95,7 +95,7 @@ pub struct IncomingBlock<B: BlockT> {
 
 /// Verify a justification of a block
 #[async_trait::async_trait]
-pub trait Verifier<B: BlockT>: Send + Sync {
+pub trait Verifier<B: BlockT>: Send {
 	/// Verify the given block data and return the `BlockImportParams` to
 	/// continue the block import process.
 	async fn verify(