Auto merge of #11299 - servo:GlutinCompositorProxy-Send, r=nox

Remove unsafe Send implementation for GlutinCompositorProxy.

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Send is now implemented for glutin::WindowProxy.

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ports/glutin/window.rs

@@ -845,9 +845,6 @@ struct GlutinCompositorProxy {
     window_proxy: Option<glutin::WindowProxy>,
 }
 
-// TODO: Should this be implemented here or upstream in glutin::WindowProxy?
-unsafe impl Send for GlutinCompositorProxy {}
-
 impl CompositorProxy for GlutinCompositorProxy {
     fn send(&self, msg: compositor_thread::Msg) {
         // Send a message and kick the OS event loop awake.