Simplify deposit_event declaration in decl_module (#3506)

* simplify module deposit_event declaration

* fix

* bump version

* fix

* fix test

* fix doc

substrate/srml/staking/src/lib.rs

@@ -674,7 +674,7 @@ decl_module! {
 		/// Number of eras that staked funds must remain bonded for.
 		const BondingDuration: EraIndex = T::BondingDuration::get();
 
-		fn deposit_event<T>() = default;
+		fn deposit_event() = default;
 
 		fn on_finalize() {
 			// Set the start of the first era.
@@ -1595,7 +1595,7 @@ impl<T, Reporter, Offender, R, O> ReportOffence<Reporter, Offender, O>
 			R::report_offence(reporters, offence)
 		} else {
 			<Module<T>>::deposit_event(
-				RawEvent::OldSlashingReportDiscarded(offence_session).into()
+				RawEvent::OldSlashingReportDiscarded(offence_session)
 			)
 		}
 	}