Make hooks and call attributes optional in pallet macro (#8853)

* Make #[pallet::hooks] optional

* Make #[pallet::call] optional

* Remove unused imports

* Update UI test expectations

* Update UI test expectations

* Remove unnecessary HooksDef::empty method

* Remove unnecessary CallDef::empty method

* Clarify what would happen when no call or hooks are specified in a pallet

substrate/frame/support/test/tests/pallet_instance.rs

@@ -209,7 +209,6 @@ pub mod pallet {
 #[frame_support::pallet]
 pub mod pallet2 {
 	use frame_support::pallet_prelude::*;
-	use frame_system::pallet_prelude::*;
 
 	#[pallet::config]
 	pub trait Config<I: 'static = ()>: frame_system::Config {
@@ -220,12 +219,6 @@ pub mod pallet2 {
 	#[pallet::generate_store(pub(crate) trait Store)]
 	pub struct Pallet<T, I = ()>(PhantomData<(T, I)>);
 
-	#[pallet::hooks]
-	impl<T: Config<I>, I: 'static> Hooks<BlockNumberFor<T>> for Pallet<T, I> {}
-
-	#[pallet::call]
-	impl<T: Config<I>, I: 'static> Pallet<T, I> {}
-
 	#[pallet::event]
 	pub enum Event<T: Config<I>, I: 'static = ()> {
 		/// Something