Reverting "Super hacky garbage attempt at handling OneShot events (removing and freeing them).  Works on and off so far, but I've seen a SEGV on quit."

This reverts commit 6593bdb4377731b2c21ca2da4c4ca0a806446a29.
Different approach to the handling of OneShots by unifying all events
into a common event map (and only a single one).

It's working (experimentally) without error, but valgrind reports some
direct memory leaks that are not allocated by EventLoop but perhaps
should be deleted by EventLoop?!  Further investigation needed...