Auto merge of #17588 - odeits:patch-1, r=SimonSapin

Fix warn stable_features

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

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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;