Remove Python 2.x and other compat

[grayjk]

No description provided.

[grayjk]

is it also now safe to remove:

tests/test_adapter_py33.py
tests/test_descriptors_py36.py
tests/test_inheritance_py37.py
tests/test_formatargspec_py35.py
tests/test_class_py37.py

[grayjk]

what about https://github.com/GrahamDumpleton/wrapt/blob/develop/setup.py#L18?

[GrahamDumpleton]

I don't believe it is safe to remove the files:

tests/test_adapter_py33.py
tests/test_descriptors_py36.py
tests/test_inheritance_py37.py
tests/test_formatargspec_py35.py
tests/test_class_py37.py

This is because the prefix says to only run these tests if the Python version matches or is greater than that in the file name suffix. So the files have to be left as is, or the tests integrated into the tests file without the version suffix.

I am probably happy just to leave the files as is at the moment rather than integrate them into non versioned test file as for now still leaves a record of which versions those tests started being valid for.

As to the `setup.py file, instead of:

    if platform.system() == "Windows" and sys.version_info[0] < 3:
        disable_extensions = True
        force_extensions = False
    else:
        disable_extensions = False
        force_extensions = False

should be okay to now use:

    disable_extensions = False
    force_extensions = False

[grayjk]

I rebased on current develop branch. Let me know if you need any changes