Simplify deposit_event declaration in decl_module (#3506)

* simplify module deposit_event declaration

* fix

* bump version

* fix

* fix test

* fix doc

substrate/srml/support/test/tests/system.rs

@@ -12,8 +12,11 @@ pub trait Trait: 'static + Eq + Clone {
 
 srml_support::decl_module! {
 	pub struct Module<T: Trait> for enum Call where origin: T::Origin {
-		pub fn deposit_event(_event: T::Event) {
-		}
+	}
+}
+
+impl<T: Trait> Module<T> {
+	pub fn deposit_event(_event: impl Into<T::Event>) {
 	}
 }
 
@@ -49,4 +52,4 @@ pub fn ensure_root<OuterOrigin, AccountId>(o: OuterOrigin) -> Result<(), &'stati
 	where OuterOrigin: Into<Result<RawOrigin<AccountId>, OuterOrigin>>
 {
 	o.into().map(|_| ()).map_err(|_| "bad origin: expected to be a root origin")
-}
+}