Remove lang_items that disappeared from new rust

src/util/lang_items.rs

@@ -16,18 +16,10 @@
 #[cfg(all(not(test), not(feature = "test")))]
 use core::fmt::Arguments;
 
-#[cfg(all(not(test), not(feature = "test")))]
-#[lang="stack_exhausted"]
-extern fn stack_exhausted() {}
-
 #[cfg(all(not(test), not(feature = "test")))]
 #[lang="eh_personality"]
 extern fn eh_personality() {}
 
-#[cfg(all(not(test), not(feature = "test")))]
-#[lang="begin_unwind"]
-extern fn begin_unwind() {}
-
 #[cfg(all(not(test), not(feature = "test")))]
 #[lang="panic_fmt"]
 pub fn panic_fmt(_fmt: &Arguments, _file_line: &(&'static str, usize)) -> ! {