Remove feature flags

Note that setting a global allocator is not yet stable, and
linked_list_allocator also requires nightly still

Author: jonas-schievink

src/lib.rs

@@ -45,8 +45,6 @@
 //! // omitted: exception handlers
 //! ```
 
-#![feature(allocator_api)]
-#![feature(const_fn)]
 #![no_std]
 
 extern crate alloc;