Bug 1560864 [wpt PR 17374] - Update interfaces/webxr.idl, a=testonly

Automatic update from web-platform-tests
Update interfaces/webxr.idl (#17374)

Source: https://github.com/tidoust/reffy-reports/blob/2bd98c3/whatwg/idl/webxr.idl
Build: https://travis-ci.org/tidoust/reffy-reports/builds/547080935
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wpt-commits: 887d08e63a19b14acf3217df77f12c121a792fed
wpt-pr: 17374

testing/web-platform/tests/interfaces/webxr.idl

@@ -203,8 +203,6 @@ dictionary XRWebGLLayerInit {
              optional XRWebGLLayerInit layerInit)]
 interface XRWebGLLayer {
   // Attributes
-  [SameObject] readonly attribute XRWebGLRenderingContext context;
-
   readonly attribute boolean antialias;
   readonly attribute boolean ignoreDepthValues;