Remove python2 shebangs where appropriate

[mariuszskon]

Closes #1404
All non-scripts have had the shebang removed.
Other than the pwnlib/commandline directory, these scripts were found (so the shebang was not removed):

pwnlib/data/useragents/download-useragents.py
pwnlib/data/syscalls/generate.py

The empty files mentioned in #1404 appear to be used. __doc__ files in shellcraft are used in

pwntools/pwnlib/shellcraft/__init__.py

Line 37 in 45eb8bc

with open(os.path.join(self._absdir, "__doc__")) as fd:

pwnlib/encoders/arm/alphanumeric/alphanumeric.py is indirectly imported through

pwntools/pwnlib/encoders/__init__.py

Line 12 in 55dfe9b

from pwnlib.encoders.encoder import alphanumeric

This means the empty files were not removed.

[mariuszskon]

Hmm, the coveralls output seems to have suddenly started considering the scripts so the coverage delta is relatively large, but I think it's a false positive.

I'm not sure what the PyLint errors are 😬

[Arusekk]

Easy, the pylint errors are due to line number changes (the simple line diff is not so great), especially that your changes are near the beginning.