kernel: remove the unused box_syntax feature request

The `box_syntax` was removed from the rust compiler and we didnt make
use of it anyway anymore.

Anyways, this fixes #96

Signed-off-by: Andy-Python-Programmer <andypythonappdeveloper@gmail.com>

Author: Andy-Python-Programmer

src/aero_kernel/src/main.rs

@@ -37,7 +37,6 @@
     linked_list_cursors,
     extern_types,
     new_uninit,
-    box_syntax,
     step_trait,
     prelude_import,
     allocator_api,