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/transaction-payment/src/mock.rs

@@ -157,14 +157,4 @@ impl Config for Runtime {
 	type WeightToFee = WeightToFee;
 	type LengthToFee = TransactionByteFee;
 	type FeeMultiplierUpdate = ();
-	type WeightInfo = ();
-}
-
-#[cfg(feature = "runtime-benchmarks")]
-pub fn new_test_ext() -> sp_io::TestExternalities {
-	crate::tests::ExtBuilder::default()
-		.base_weight(Weight::from_parts(100, 0))
-		.byte_fee(10)
-		.balance_factor(0)
-		.build()
 }