servo: Merge #9920 - Remove unused cell_extras feature gates. Fixes #9912 (from vishy1618:issue_9912); r=Ms2ger

Source-Repo: https://github.com/servo/servo
Source-Revision: a96b2360a9e6cfed26c101704fd4c804ed1fcfd3

servo/components/layout/lib.rs

@@ -4,7 +4,6 @@
 
 #![feature(as_unsafe_cell)]
 #![feature(box_syntax)]
-#![feature(cell_extras)]
 #![feature(custom_derive)]
 #![feature(mpsc_select)]
 #![feature(nonzero)]

servo/components/script/lib.rs

@@ -6,7 +6,6 @@
 #![feature(as_unsafe_cell)]
 #![feature(borrow_state)]
 #![feature(box_syntax)]
-#![feature(cell_extras)]
 #![feature(const_fn)]
 #![feature(core_intrinsics)]
 #![feature(custom_attribute)]

servo/components/style/lib.rs

@@ -4,7 +4,6 @@
 
 #![feature(box_syntax)]
 #![feature(box_patterns)]
-#![feature(cell_extras)]
 #![feature(concat_idents)]
 #![feature(core_intrinsics)]
 #![feature(custom_attribute)]