servo: Merge #17588 - Fix warn stable_features (from odeits:patch-1); r=SimonSapin

struct_field_attributes has been stable since 1.20.0. Attribute no longer needed.

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Source-Repo: https://github.com/servo/servo
Source-Revision: fd65ac8924dd75b1f80e2cf048f64e11d3387976

--HG--
extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
extra : subtree_revision : 282a6adb57bfc4fedf8a991b29cb480fb5464464

servo/ports/glutin/lib.rs

@@ -5,7 +5,6 @@
 //! A simple application that uses glutin to open a window for Servo to display in.
 
 #![feature(box_syntax)]
-#![feature(struct_field_attributes)]
 
 #[macro_use] extern crate bitflags;
 extern crate compositing;