Relax BoundedVec trait restrictions (#8749)

* requiring users to maintain an unchecked invariant is unsafe

* relax trait restrictions on BoundedVec<T, S>

A normal `Vec<T>` can do many things without any particular trait
bounds on `T`. This commit relaxes the bounds on `BoundedVec<T, S>`
to give it similar capabilities.

substrate/frame/support/src/lib.rs

@@ -1238,7 +1238,7 @@ pub mod pallet_prelude {
 		dispatch::{DispatchResultWithPostInfo, Parameter, DispatchError, DispatchResult},
 		weights::{DispatchClass, Pays, Weight},
 		storage::types::{StorageValue, StorageMap, StorageDoubleMap, ValueQuery, OptionQuery},
-		storage::bounded_vec::{BoundedVec, BoundedVecValue},
+		storage::bounded_vec::BoundedVec,
 	};
 	pub use codec::{Encode, Decode};
 	pub use crate::inherent::{InherentData, InherentIdentifier, ProvideInherent};