Remove unused feature gates (#118)

Aaron1011 · web-flow · commit 206ecfb96a22 · 2020-05-22T10:58:16.000+02:00
This crate is able to compile without any of these enabled.
diff --git a/src/main.rs b/src/main.rs
@@ -1,9 +1,6 @@
 #![feature(lang_items)]
 #![feature(global_asm)]
-#![feature(step_trait)]
 #![feature(llvm_asm)]
-#![feature(nll)]
-#![feature(const_fn)]
 #![no_std]
 #![no_main]
 
