Remove six again
Remove six again

The six library has been removed once in change
Id572aec8a6fda7676eb03d17c66fd33f9801f25d. However it was added back in
Ic106bee4fc3f5c401c4f8d8ecb1c4e735560bcc2.

This change removes six again.

Change-Id: Ib7300cfb4fd8d8c81cff780fbdb44d537e29680a
Signed-off-by: Takashi Natsume <2c48eb5bf73c355a2d5583bc776dffa383cdf819@gmail.com>

ChameleonCloud/blazar,ChameleonCloud/blazar,openstack/blazar,openstack/blazar