servo: Merge #17554 - Stop using the unstable optin_builtin_traits feature (from mbrubeck:oibit); r=ManishEarth

- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix part of #5286.
- [x] These changes do not require tests because they are refactoring only.

Source-Repo: https://github.com/servo/servo
Source-Revision: 6d7fdb484b42a26f9d33217e163f157fd87b6742

servo/components/script/lib.rs

@@ -9,7 +9,6 @@
 #![feature(mpsc_select)]
 #![feature(nonzero)]
 #![feature(on_unimplemented)]
-#![feature(optin_builtin_traits)]
 #![feature(option_entry)]
 #![feature(plugin)]
 #![feature(proc_macro)]