Eliminate experimental feature (#3654)

Totally removes the `experimental` feature. Closes #3648.

---------

Co-authored-by: Bastian Köcher <git@kchr.de>

cumulus/parachains/runtimes/contracts/contracts-rococo/Cargo.toml

@@ -196,8 +196,6 @@ try-runtime = [
 	"sp-runtime/try-runtime",
 ]
 
-experimental = ["pallet-aura/experimental"]
-
 # A feature that should be enabled when the runtime should be built for on-chain
 # deployment. This will disable stuff that shouldn't be part of the on-chain wasm
 # to make it smaller, like logging for example.

cumulus/parachains/runtimes/contracts/contracts-rococo/src/lib.rs

@@ -193,10 +193,7 @@ impl pallet_timestamp::Config for Runtime {
 	/// A timestamp: milliseconds since the unix epoch.
 	type Moment = u64;
 	type OnTimestampSet = Aura;
-	#[cfg(feature = "experimental")]
 	type MinimumPeriod = ConstU64<0>;
-	#[cfg(not(feature = "experimental"))]
-	type MinimumPeriod = ConstU64<{ SLOT_DURATION / 2 }>;
 	type WeightInfo = pallet_timestamp::weights::SubstrateWeight<Runtime>;
 }
 
@@ -349,7 +346,6 @@ impl pallet_aura::Config for Runtime {
 	type DisabledValidators = ();
 	type MaxAuthorities = ConstU32<100_000>;
 	type AllowMultipleBlocksPerSlot = ConstBool<true>;
-	#[cfg(feature = "experimental")]
 	type SlotDuration = ConstU64<SLOT_DURATION>;
 }