Remove use of trait Store (#2286)

* Remove use of Store trait from xcmp-queue pallet

* Remove Store trait usage from dmp-queue pallet

* Remove Store trait usage from parachain-system pallet

* Remove use of Store trait from cumulus

* Run cargo fmt

test/runtime/src/test_pallet.rs

@@ -23,7 +23,6 @@ pub mod pallet {
 	use frame_system::pallet_prelude::*;
 
 	#[pallet::pallet]
-	#[pallet::generate_store(pub(super) trait Store)]
 	pub struct Pallet<T>(_);
 
 	#[pallet::config]