[archive] remove _TarFile wrapper class

[bmr-cymru]

The sos.archive submodule contains a wrapper for the tarfile.TarFile class:

# Compatibility version of the tarfile.TarFile class. This exists to allow
# compatibility with PY2 runtimes that lack the 'filter' parameter to the
# TarFile.add() method. The wrapper class is used on python2.6 and earlier
# only; all later versions include 'filter' and the native TarFile class is
# used directly.
class _TarFile(tarfile.TarFile):

    # Taken from the python 2.7.5 tarfile.py
    def add(self, name, arcname=None, recursive=True,
            exclude=None, filter=None):
        """Add the file `name' to the archive. `name' may be any type of file
           (directory, fifo, symbolic link, etc.). If given, `arcname'
           specifies an alternative name for the file in the archive.
           Directories are added recursively by default. This can be avoided by
           setting `recursive' to False. `exclude' is a function that should
           return True for each filename to be excluded. `filter' is a function
           that expects a TarInfo object argument and returns the changed
           TarInfo object, if it returns None the TarInfo object will be
           excluded from the archive.
        """

Since the earliest 2.x release we test with now is Python-2.7 this can now be removed and the module simplified to just rely on the regular TarFile implementation.