mesa/main: do not allow astc enums on gles1

mesa/main: do not allow astc enums on gles1

ctx->Extensions.KHR_texture_compression_astc_ldr is set regardless of
the API that's used, so checking for those direcly will always enable
extensions when they are supported by the driver.

But there's no extension enabling ASTC for OpenGL ES 1.x, so we
shouldn't allow those enums there.

Signed-off-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>