Remove shebang and executable bit from tarfile module about cpython

[jaraco]

In the prior bug, gpshead indicated that these shebangs should probably be removed.

@serhiy-storchaka Do you have any objections to removing executable bits and shebang from tarfile and maybe others?

[serhiy-storchaka]

I think it made more sense in the past, when:

• python -m did not exist.
• There was usually only one system Python.
• Python module (like pydoc) could be turned into a command by a symlink.
• In general, the stdlib code supported compatibility with several Python versions.

Today this is perhaps no longer relevant or less relevant. But it needs to be discussed with a wider audience to shape general policy.