Remove needless returns detected by clippy in the compiler

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -2553,7 +2553,7 @@ impl<'a> Parser<'a> {
                 err.delay_as_bug();
             }
         }
-        return Ok(false); // Don't continue.
+        Ok(false) // Don't continue.
     }
 
     /// Attempt to parse a generic const argument that has not been enclosed in braces.

compiler/rustc_parse/src/parser/item.rs

@@ -457,7 +457,7 @@ impl<'a> Parser<'a> {
 
     fn parse_item_builtin(&mut self) -> PResult<'a, Option<ItemInfo>> {
         // To be expanded
-        return Ok(None);
+        Ok(None)
     }
 
     /// Parses an item macro, e.g., `item!();`.