librustc: Stop parsing modes and remove them entirely from the language

src/libcore/stackwalk.rs

@@ -81,6 +81,6 @@ fn frame_address(f: &fn(x: *u8)) {
 pub mod rusti {
     #[abi = "rust-intrinsic"]
     pub extern "rust-intrinsic" {
-        pub fn frame_address(+f: &once fn(x: *u8));
+        pub fn frame_address(f: &once fn(x: *u8));
     }
 }