Move Python test files in the test directory

Rationale: the scripts have also been modified to fetch the
libneubot.py installed at /usr/local/share/libneubot, allowing
us to test the installed libneubot.py.

On the contrary, when these files were in the toplevel dir, they
fetched ./libneubot.py, therefore, we had not the guarantee of
installing a good and valid copy of libneubot.py.

While there, zap a useless import.