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/metadata-ir/src/v14.rs

@@ -20,8 +20,8 @@
 use super::types::{
 	ExtrinsicMetadataIR, MetadataIR, PalletCallMetadataIR, PalletConstantMetadataIR,
 	PalletErrorMetadataIR, PalletEventMetadataIR, PalletMetadataIR, PalletStorageMetadataIR,
-	StorageEntryMetadataIR, StorageEntryModifierIR, StorageEntryTypeIR, StorageHasherIR,
-	TransactionExtensionMetadataIR,
+	SignedExtensionMetadataIR, StorageEntryMetadataIR, StorageEntryModifierIR, StorageEntryTypeIR,
+	StorageHasherIR,
 };
 
 use frame_metadata::v14::{
@@ -137,8 +137,8 @@ impl From<PalletErrorMetadataIR> for PalletErrorMetadata {
 	}
 }
 
-impl From<TransactionExtensionMetadataIR> for SignedExtensionMetadata {
-	fn from(ir: TransactionExtensionMetadataIR) -> Self {
+impl From<SignedExtensionMetadataIR> for SignedExtensionMetadata {
+	fn from(ir: SignedExtensionMetadataIR) -> Self {
 		SignedExtensionMetadata {
 			identifier: ir.identifier,
 			ty: ir.ty,
@@ -152,7 +152,7 @@ impl From<ExtrinsicMetadataIR> for ExtrinsicMetadata {
 		ExtrinsicMetadata {
 			ty: ir.ty,
 			version: ir.version,
-			signed_extensions: ir.extensions.into_iter().map(Into::into).collect(),
+			signed_extensions: ir.signed_extensions.into_iter().map(Into::into).collect(),
 		}
 	}
 }