obs-browser: Do not use WasHidden() for visibility on 3507+
Using WasHidden() for the purposes of visibility no longer can be relied
upon due to some sort of bug with OSR in Chromium. This issue does not
happen when using 3440. The browser works fine without WasHidden()
calls, so we must remove its usage or be forced to use 3440. For those
who need the visibility handling, an alternative will have to be used
once it's available.
Additionally, this reverts the failed workaround to use OBS FPS in place
of SignalBeginFrame() because that code is no longer needed due to the
WasHidden() removal.
jp9000