This reverts commit 8d520b97.

This can actually cause a hard lock due to the windows API when
destroying window capture.  When the graphics thread locks the source
list for doing tick or render, and then the UI thread tries to destroy a
source, the UI thread will wait for the graphics thread to complete
rendering/ticking of sources.  The video_tick of window capture would
then check windows in the same process and try to query the window's
name via GetWindowText.  However, GetWindowText is synchronous, and will
not return until the window event has been processed by the UI thread,
so it will perpetually lock because the two threads are waiting for each
other to finish.