Auto merge of rust-lang#10624 - the8472:remove-drain-filter-feature, r=xFrednet

remove unusued `#![feature(drain_filter)]`

The unstable feature does not appear to be used and its presence blocks work in rust-lang#104455

changelog: none

Author: bors

clippy_lints/src/lib.rs

@@ -1,7 +1,6 @@
 #![feature(array_windows)]
 #![feature(binary_heap_into_iter_sorted)]
 #![feature(box_patterns)]
-#![feature(drain_filter)]
 #![feature(if_let_guard)]
 #![feature(iter_intersperse)]
 #![feature(let_chains)]