Remove old python version support

[sidler-mozilla]

https://github.com/mozilla-iam/mozilla-aws-cli/blob/master/setup.py#L35-L46

Are all these versions really necessary? I suggest moving to python3.6, 3.7 and 3.8 and call it good. Doing so would allow you to use more modern features such as f-strings. The biggest reason would be the impending deprecation of python2. Also are any distros shipping with python3.4 or 3.5? If not, why support?

[gene1wood]

Are all these versions really necessary?

Ya, we wanted to make sure to support Python 2 given the OSs that are still supported and which don't have Python 3.

Also are any distros shipping with python3.4 or 3.5? If not, why support?

The general goal, since this is an end user tool that runs on folks laptops, is to support as broad a user base as possible. Indeed 2.7 and 3.4 have reached end of life but I'd like to try to make installation as low-friction as possible. I can imagine removing some supported versions down the road though.

[gene1wood]

Given we're now 2 years beyond the Python 2.7 end of life of January 1, 2020 I think we're good to remove support for it now.