Remove needless lifetimes

src/libsyntax_ext/assert.rs

@@ -131,7 +131,7 @@ fn parse_assert<'a>(
     Ok(Assert { cond_expr, custom_message })
 }
 
-fn parse_custom_message<'a>(parser: &mut Parser<'a>) -> Option<TokenStream> {
+fn parse_custom_message(parser: &mut Parser<'_>) -> Option<TokenStream> {
     let ts = parser.parse_tokens();
     if !ts.is_empty() {
         Some(ts)