As pointed out in WebGL issue 3014, ANGLE has been exposing ETC1
texture support on desktop GL when GL_ARB_ES3_compatibility or GL
4.3+ is available. However, it is very likely that none of these
platforms actually have hardware support for this format, and are
only supporting it for compatiblity with ES3. We shouldn't expose
this so that desktop clients can use a better format instead.

Bug: chromium:1048244
Change-Id: I53837a05719d0ca3ff390b5b45b61a1f9c72a535
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2687466Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jonah Ryan-Davis <jonahr@google.com>