Remove XRWebGLLayer.requestViewportScaling()

Viewport scaling has been removed from the WebXR spec, so removing
before the API is released.

Bug: 961436
Change-Id: I9f1bbb7dde8971d1c659592b7d3b23e14a17b928
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1620908
Reviewed-by: Brandon Jones <bajones@chromium.org>
Reviewed-by: Alexander Cooper <alcooper@chromium.org>
Commit-Queue: Bill Orr <billorr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661504}
7 files changed