Cleanup required dependencies

[philipptrenz]

We noticed that in pyproject.toml click and pytz are listed as required dependencies. However, click seems to be not used in the project at all and pytz only in unit tests.

I would therefore recommend to:

a) Remove click dependency
b) Move pytz to the optional testing dependencies

Any objections?

[Flix6x]

No objections here.

And pytz should probably not be needed any more, since Python 3.9 and up supports timezones in its standard lib.

[philipptrenz]

Thanks @Flix6x, I'll create a PR.