obs-browser: Fix browser panel crash

Reverts the container widget, then decouples the browser's window handle
from its parent instead.  This allows calling DestroyBrowser() safely.

obs-browser @ 00c9fdb9

-Subproject commit 8580b491bc6471c3adc3503b944ca3c8b7e0db7e
+Subproject commit 00c9fdb93339ba3234e1a1f094e4487fe0a7984c