ci/angle: remove USE_ANGLE variable

Now that every ANGLE use is covered by tag consistency checks
(structured tagging), we don't need the USE_ANGLE flag anymore, because
if we have ANGLE_TAG set, it means that ANGLE is required in this job.

In detail, it means that the test job has inherited ANGLE_TAG from
`.container-builds-angle`.

Signed-off-by: Guilherme Gallo <guilherme.gallo@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33421>
7 files changed