Officially drop support for Python 2

[workhorsy]

Reasons to drop 2:

1. It is an absolute nightmare to have to test all the different versions (32bit/64bit, python2/python3, windows/linux/osx/bsd/solaris/haiku). By removing python 2 support, it greatly reduces the number of things to test.
2. It has been 16 years since Python 3 was announced. People have had enough time to migrate.
3. Python 2 support officially ended in 2021.
4. We are starting to get deprecation warnings.
5. We can start using new features of 3
6. We will only have to support 3.7 and up, because Python only supports 5 years of old versions now
7. People can still use py-cpuinfo version 8.0 on python 2

Reasons to keep 2:

1. According to PyPi about 1% to 3% of users still use 2.7 for py-cpuinfo: https://pypistats.org/packages/py-cpuinfo

[workhorsy]

Fixed in #179