Fix lint

[zpuskas]

Running pylfakes reveals several QA issues with the code:

>>> pyflakes .
./tests/myStringIO.py:4:5 'io.StringIO' imported but unused
./tests/test_trash_rm.py:3:1 'six' imported but unused
./tests/test_trash_rm.py:5:1 'mock.call' imported but unused
./tests/empty/test_empty_end_to_end_interactive.py:7:1 '..support.list_trash_dir' imported but unused
./tests/put/test_file_trasher.py:6:1 'trashcli.put.Trasher' imported but unused
./tests/put/test_home_fallback.py:6:1 'trashcli.put.Trasher' imported but unused
./trashcli/list.py:7:1 '.fstab.volume_of' imported but unused
./trashcli/list.py:39:18 redefinition of unused 'volume_of' from line 7
./trashcli/list.py:131:59 redefinition of unused 'volume_of' from line 7

This PR will:

• Fix lint in tests
• Fix lint in trash-cli

Test plan:

>>> python -m unittest discover -v
...
----------------------------------------------------------------------
Ran 280 tests in 13.362s

OK
>>> pyflakes .
>>>