Remove the control_flow_enum feature from clippy

Author: scottmcm

Diff for: src/tools/clippy/clippy_utils/src/lib.rs

@@ -1,6 +1,5 @@
 #![feature(array_chunks)]
 #![feature(box_patterns)]
-#![feature(control_flow_enum)]
 #![feature(f128)]
 #![feature(f16)]
 #![feature(if_let_guard)]