tests/docker: Remove obsolete VirGL --with-glx configure option

The GLX configure option has been removed in 71c75f201d [*].
We missed that when updating to v0.7.0 in commit fab3220f.

This silents:

  configure: creating ./config.status
  config.status: creating virglrenderer.pc
  ...
  configure: WARNING: unrecognized options: --with-glx

[*] https://gitlab.freedesktop.org/virgl/virglrenderer/commit/71c75f201d



Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20200212202709.12665-3-philmd@redhat.com>
Message-Id: <20200316172155.971-4-alex.bennee@linaro.org>