Remove RenderbufferImpl.cpp BUG=angleproject:970 Change-Id: I1606df42e6423fe84d3ab69029a37224adb89a9b Reviewed-on: https://chromium-review.googlesource.com/286552 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org> Tested-by: Geoff Lang <geofflang@chromium.org>