backends/drm: don't permanently disable VRR when the test commit fails

In 5.24, the same code path is used for testing direct scanout, so that
causes false negatives. Generally though, the user setting shouldn't be
touched, it's not really proper feedback for the driver or KWin having
problems.

src/backends/drm/drm_output.cpp

@@ -317,7 +317,6 @@ bool DrmOutput::present()
             m_pipeline->applyPendingChanges();
         } else {
             m_pipeline->revertPendingChanges();
-            setVrrPolicy(RenderLoop::VrrPolicy::Never);
         }
     }
     bool modeset = gpu()->needsModeset();