Switch All construct_runtimes to New Syntax (#2979)

Clean up all the old syntax.

---------

Co-authored-by: command-bot <>
Co-authored-by: gupnik <nikhilgupta.iitk@gmail.com>
Co-authored-by: Nikhil Gupta <17176722+gupnik@users.noreply.github.com>
Co-authored-by: Maksym H <1177472+mordamax@users.noreply.github.com>

docs/sdk/src/guides/your_first_pallet/mod.rs

@@ -428,8 +428,8 @@ pub mod pallet {
 			use crate::guides::your_first_pallet::pallet as pallet_currency;
 
 			construct_runtime!(
-				pub struct Runtime {
-					// ---^^^^^^ This is where `struct Runtime` is defined.
+				pub enum Runtime {
+					// ---^^^^^^ This is where `enum Runtime` is defined.
 					System: frame_system,
 					Currency: pallet_currency,
 				}
@@ -708,7 +708,7 @@ pub mod pallet_v2 {
 			use crate::guides::your_first_pallet::pallet_v2 as pallet_currency;
 
 			construct_runtime!(
-				pub struct Runtime {
+				pub enum Runtime {
 					System: frame_system,
 					Currency: pallet_currency,
 				}

docs/sdk/src/polkadot_sdk/cumulus.rs

@@ -55,7 +55,7 @@ mod tests {
 
 		#[docify::export(CR)]
 		construct_runtime!(
-			pub struct Runtime {
+			pub enum Runtime {
 				// system-level pallets.
 				System: frame_system,
 				Timestamp: pallet_timestamp,

docs/sdk/src/polkadot_sdk/frame_runtime.rs

@@ -156,9 +156,9 @@ mod tests {
 		use super::pallet as pallet_example;
 		use frame::{prelude::*, testing_prelude::*};
 
-		// The major macro that amalgamates pallets into `struct Runtime`
+		// The major macro that amalgamates pallets into `enum Runtime`
 		construct_runtime!(
-			pub struct Runtime {
+			pub enum Runtime {
 				System: frame_system,
 				Example: pallet_example,
 			}