SF: Fix memory leak in HdrSdrRatioOverlay

Added a utility function to release GraphicBuffer from SurfaceComposerClient caches.

Updated destructors in `RefreshRateOverlay` and `HdrSdrRatioOverlay`
to use this function. This ensures buffers are consistently unregistered
from SurfaceComposerClient, preventing memory leaks when overlays are
destroyed.

Bug: 439480487
Test: Enabled and disabled RefreshRateOverlay and HdrSdrRatioOverlay multiple times, verified no memory leaks in logcat.
Flag: EXEMPT bug fix
Change-Id: I9810657ee52646ba75f656cf82388b47aacef72d