Clean up imports and kill port of logging.WatchedFileHandler

There were a bunch of places where we were using continuation lines for
multiple lines of imports from the same module. I've cleaned those up to use
parentheses, instead.

While I was doing this, I noticed that we still had a backport of
logging.WatchedFileHandler. Since we're now 2.6+ only, we don't need this
anymore.

Testing done: Ran unit tests
Reviewed at https://reviews.reviewboard.org/r/4914/