Remove #[alloc_error_handler] from the compiler and library

Author: Amanieu

crates/hir-def/src/builtin_attr.rs

@@ -381,10 +381,6 @@ pub const INERT_ATTRIBUTES: &[BuiltinAttribute] = &[
 
     rustc_attr!(rustc_allocator, Normal, template!(Word), WarnFollowing, IMPL_DETAIL),
     rustc_attr!(rustc_nounwind, Normal, template!(Word), WarnFollowing, IMPL_DETAIL),
-    gated!(
-        alloc_error_handler, Normal, template!(Word), WarnFollowing,
-        experimental!(alloc_error_handler)
-    ),
     gated!(
         default_lib_allocator, Normal, template!(Word), WarnFollowing, allocator_internals,
         experimental!(default_lib_allocator),