Revert "FRAME: Create TransactionExtension as a replacement for SignedExtension (#2280)" (#3665)

This PR reverts #2280 which introduced `TransactionExtension` to replace
`SignedExtension`.

As a result of the discussion
[here](https://github.com/paritytech/polkadot-sdk/pull/3623#issuecomment-1986789700),
the changes will be reverted for now with plans to reintroduce the
concept in the future.

---------

Signed-off-by: georgepisaltu <george.pisaltu@parity.io>

substrate/frame/support/src/lib.rs

@@ -54,8 +54,7 @@ pub mod __private {
 	#[cfg(feature = "std")]
 	pub use sp_runtime::{bounded_btree_map, bounded_vec};
 	pub use sp_runtime::{
-		traits::{AsSystemOriginSigner, Dispatchable},
-		DispatchError, RuntimeDebug, StateVersion, TransactionOutcome,
+		traits::Dispatchable, DispatchError, RuntimeDebug, StateVersion, TransactionOutcome,
 	};
 	#[cfg(feature = "std")]
 	pub use sp_state_machine::BasicExternalities;
@@ -76,7 +75,6 @@ pub mod storage;
 #[cfg(test)]
 mod tests;
 pub mod traits;
-pub mod transaction_extensions;
 pub mod weights;
 #[doc(hidden)]
 pub mod unsigned {
@@ -1586,8 +1584,8 @@ pub mod pallet_macros {
 	/// [`ValidateUnsigned`](frame_support::pallet_prelude::ValidateUnsigned) for
 	/// type `Pallet<T>`, and some optional where clause.
 	///
-	/// NOTE: There is also the [`sp_runtime::traits::TransactionExtension`] trait that can be
-	/// used to add some specific logic for transaction validation.
+	/// NOTE: There is also the [`sp_runtime::traits::SignedExtension`] trait that can be used
+	/// to add some specific logic for transaction validation.
 	///
 	/// ## Macro expansion
 	///