Remove DisplayGbm and SurfaceGbm. The Gbm classes were used to emulate WindowSurfaces on ChromeOS for testing. These emulated features are not used in any shipping configuration and cause issues because ANGLE opens drm devices uneccessarily. Bug: chromium:1344962 Change-Id: If564e40744f7825035bbbd63c141b154c534ed72 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4023096 Reviewed-by: Yuly Novikov <ynovikov@chromium.org> Commit-Queue: Yuly Novikov <ynovikov@chromium.org> Reviewed-by: Brian Ho <hob@chromium.org>