Drop long/deep path extra support code

[pombredanne]

The latest Python 3.6 now support deep paths on Windows according to https://docs.python.org/3/using/windows.html#removing-the-max-path-limitation

Therefore, I would likely to drop entirely support of "UNC" paths that was added to to support deep paths on Windows and instead only supports this on Python 3.6 with the registry setting explained here: https://docs.python.org/3/using/windows.html#removing-the-max-path-limitation

[pombredanne]

This is fixed in https://github.com/nexB/aboutcode-toolkit/tree/361-make-transform-work branch