Revert "build: add test-gl-renderer option"

This reverts commit 1618697d.

The original commit was a workaround for
mesa/mesa#2219

 which was fixed
in Mesa:
- c7617d8908a970124321ce731b43d5996c3c5775 released as 20.1.0-rc1
- a0e6341fe4417e41cda0b19e4fa7f8bbe4e1dba1 released as 19.3.5
- f27e5d9df5bc9c85d45c2cb1f2a4997b453365fe released as 20.0.0

This workaround should not be necessary anymore, we don't use it in our
CI, and it was manual to begin with. Therefore remove it.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>