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/traits/dispatch.rs

@@ -482,7 +482,7 @@ pub trait OriginTrait: Sized {
 	type Call;
 
 	/// The caller origin, overarching type of all pallets origins.
-	type PalletsOrigin: Send + Sync + Into<Self> + CallerTrait<Self::AccountId> + MaxEncodedLen;
+	type PalletsOrigin: Into<Self> + CallerTrait<Self::AccountId> + MaxEncodedLen;
 
 	/// The AccountId used across the system.
 	type AccountId;
@@ -496,14 +496,6 @@ pub trait OriginTrait: Sized {
 	/// Replace the caller with caller from the other origin
 	fn set_caller_from(&mut self, other: impl Into<Self>);
 
-	/// Replace the caller with caller from the other origin
-	fn set_caller(&mut self, caller: Self::PalletsOrigin);
-
-	/// Replace the caller with caller from the other origin
-	fn set_caller_from_signed(&mut self, caller_account: Self::AccountId) {
-		self.set_caller(Self::PalletsOrigin::from(RawOrigin::Signed(caller_account)))
-	}
-
 	/// Filter the call if caller is not root, if false is returned then the call must be filtered
 	/// out.
 	///
@@ -552,17 +544,6 @@ pub trait OriginTrait: Sized {
 	fn as_system_ref(&self) -> Option<&RawOrigin<Self::AccountId>> {
 		self.caller().as_system_ref()
 	}
-
-	/// Extract a reference to the sytsem signer, if that's what the caller is.
-	fn as_system_signer(&self) -> Option<&Self::AccountId> {
-		self.caller().as_system_ref().and_then(|s| {
-			if let RawOrigin::Signed(ref who) = s {
-				Some(who)
-			} else {
-				None
-			}
-		})
-	}
 }
 
 #[cfg(test)]

substrate/frame/support/src/traits/misc.rs

@@ -919,13 +919,24 @@ pub trait ExtrinsicCall: sp_runtime::traits::Extrinsic {
 	fn call(&self) -> &Self::Call;
 }
 
+#[cfg(feature = "std")]
+impl<Call, Extra> ExtrinsicCall for sp_runtime::testing::TestXt<Call, Extra>
+where
+	Call: codec::Codec + Sync + Send + TypeInfo,
+	Extra: TypeInfo,
+{
+	fn call(&self) -> &Self::Call {
+		&self.call
+	}
+}
+
 impl<Address, Call, Signature, Extra> ExtrinsicCall
 	for sp_runtime::generic::UncheckedExtrinsic<Address, Call, Signature, Extra>
 where
 	Address: TypeInfo,
 	Call: TypeInfo,
 	Signature: TypeInfo,
-	Extra: TypeInfo,
+	Extra: sp_runtime::traits::SignedExtension + TypeInfo,
 {
 	fn call(&self) -> &Self::Call {
 		&self.function