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>

cumulus/parachains/runtimes/bridge-hubs/bridge-hub-rococo/tests/snowbridge.rs

@@ -22,7 +22,7 @@ use bridge_hub_rococo_runtime::{
 	bridge_to_westend_config::OnBridgeHubRococoRefundBridgeHubWestendMessages,
 	xcm_config::XcmConfig, AllPalletsWithoutSystem, BridgeRejectObsoleteHeadersAndMessages,
 	Executive, MessageQueueServiceWeight, Runtime, RuntimeCall, RuntimeEvent, SessionKeys,
-	TxExtension, UncheckedExtrinsic,
+	SignedExtra, UncheckedExtrinsic,
 };
 use codec::{Decode, Encode};
 use cumulus_primitives_core::XcmError::{FailedToTransactAsset, NotHoldingFees};
@@ -171,7 +171,7 @@ fn construct_extrinsic(
 	call: RuntimeCall,
 ) -> UncheckedExtrinsic {
 	let account_id = AccountId32::from(sender.public());
-	let tx_ext: TxExtension = (
+	let extra: SignedExtra = (
 		frame_system::CheckNonZeroSender::<Runtime>::new(),
 		frame_system::CheckSpecVersion::<Runtime>::new(),
 		frame_system::CheckTxVersion::<Runtime>::new(),
@@ -188,13 +188,13 @@ fn construct_extrinsic(
 			OnBridgeHubRococoRefundRococoBulletinMessages::default(),
 		),
 	);
-	let payload = SignedPayload::new(call.clone(), tx_ext.clone()).unwrap();
+	let payload = SignedPayload::new(call.clone(), extra.clone()).unwrap();
 	let signature = payload.using_encoded(|e| sender.sign(e));
 	UncheckedExtrinsic::new_signed(
 		call,
 		account_id.into(),
 		Signature::Sr25519(signature.clone()),
-		tx_ext,
+		extra,
 	)
 }