Due to our extra logic that only exposes OES_texture_float if the format
is renderable, it's possible that the OES_texture_float_linear can be
exposed without OES_texture_float.  Make sure that can't happen.

BUG=angleproject:1145

Change-Id: I9b1262a39872abf4654d4e4751706679e24926f3
Reviewed-on: https://chromium-review.googlesource.com/322690Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>