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/primitives/runtime/src/transaction_validity.rs

@@ -82,8 +82,6 @@ pub enum InvalidTransaction {
 	MandatoryValidation,
 	/// The sending address is disabled or known to be invalid.
 	BadSigner,
-	/// The implicit data was unable to be calculated.
-	IndeterminateImplicit,
 }
 
 impl InvalidTransaction {
@@ -115,8 +113,6 @@ impl From<InvalidTransaction> for &'static str {
 				"Transaction dispatch is mandatory; transactions must not be validated.",
 			InvalidTransaction::Custom(_) => "InvalidTransaction custom error",
 			InvalidTransaction::BadSigner => "Invalid signing address",
-			InvalidTransaction::IndeterminateImplicit =>
-				"The implicit data was unable to be calculated",
 		}
 	}
 }
@@ -342,7 +338,7 @@ pub struct ValidTransactionBuilder {
 impl ValidTransactionBuilder {
 	/// Set the priority of a transaction.
 	///
-	/// Note that the final priority for `FRAME` is combined from all `TransactionExtension`s.
+	/// Note that the final priority for `FRAME` is combined from all `SignedExtension`s.
 	/// Most likely for unsigned transactions you want the priority to be higher
 	/// than for regular transactions. We recommend exposing a base priority for unsigned
 	/// transactions as a runtime module parameter, so that the runtime can tune inter-module