Switch to use f-strings.

[icemac]

I called pyupgrade --py3-only --py3-plus --py36-plus --py37-plus on
the Python files.
While looking through the changes, I did some adoptions to sometimes
use f-strings in places where the tool did not use them.

Additionally pyupgrade removed some Python 2 compatiblity leftovers.

[jugmac00]

@icemac

I called pyupgrade --py3-only --py3-plus --py36-plus --py37-plus on the Python files.

Does that mean Zope 5 does not support Python 3.6 any more?

[dataflake]

No it doesn't. I am guessing that was either a typo or just done unintentionally. But either way, if you look at https://pypi.org/project/pyupgrade/ and search for any mention of --py37-plus then all you will find is something having to do with one kind of __future__ import.

[icemac]

I've never used generator_stop which is removed by --py37-plus and it is not in the diff. But you are right, I should not have used this option in the first place.