this existed for historical reasons, but realistically now it should
be possible to build mesa with dri3 always enabled. additionally,
this check was often used as a substitute for having drm functionality,
which is sort of similar but also not really a direct match
this simplifies a bunch of conditionals and prevents users from footgunnning
themselves into orbit
Reviewed-by: Adam Jackson <ajax@redhat.com>
Reviewed-by: Eric Engestrom <eric@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30952>
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