autoreload: Don't close the IOLoop on reload

autoreload: Don't close the IOLoop on reload

This was a last-ditch effort to close file descriptors that were not
marked as CLOEXEC. However, it was never complete (it didn't touch
file descriptors that were not registered on the IOLoop), and it can't
work with asyncio (which does not allow closing the IOLoop without
stopping it and unwinding the stack first). Since Tornado (and
hopefully all major libraries using the IOLoop) is careful about
setting CLOEXEC when needed, just get rid of the close.

Fixes #1543