Show logs in the correct Jupyter notebook cell

[rossjjennings]

Fixes #1951. The problem where logging messages were shown in the incorrect cell (the cell where pint.logging.setup() was called) seems to have been caused by passing the enqueue=True option to Loguru's logger.add() function. This PR simply removes the option. I've confirmed that this works both in a newer environment that showed the issue, and in an older one, which didn't have this issue, even with enqueue=True.

I'm not sure why we were using enqueue=True to begin with. The docstring for logger.add() says this about it:

enqueue : |bool|, optional
    Whether the messages to be logged should first pass through a multiprocessing-safe queue
    before reaching the sink. This is useful while logging to a file through multiple
    processes. This also has the advantage of making logging calls non-blocking.

Hopefully getting rid of this option (and switching back to enqueue=False, which is the default in Loguru) will not cause issues in some use case I'm not aware of involving multiple PINT processes trying to log to a single file. But I think most likely this option was originally added in an attempt to get logging in a Jupyter notebook to work better, which is now backfiring.