drm-tests: null_platform_test: clean up after test finishes

We should really do this to be consistent with other tests.

BUG=none
TEST=null_platform_test still passes

Change-Id: I9041a41aa9a51dabe84a3726d88c6438f23d1bfd
Reviewed-on: https://chromium-review.googlesource.com/452545
Commit-Ready: Gurchetan Singh <gurchetansingh@chromium.org>
Tested-by: Gurchetan Singh <gurchetansingh@chromium.org>
Reviewed-by: Ilja H. Friedel <ihf@chromium.org>
1 file changed