Remove Webview Overlays on destroy

When WebViewFunctor is destroyed, overlays needs to be removed.
Bug: 194393522
Test: toggle fullscreen during video playing, and run "adb shell dumpsys
SurfaceFlinger | grep Webview", it should only show onlyi one surface
control

Change-Id: I40d0e503c4f5b25c59886820485e7734716ac859