Remove explicit distribute depend.

Causes issues with the recent re-merge with setuptools. Advice from
upstream is to stop doing explicit depends.

Change-Id: Ic83dca8c17799335b76311d1d657adcd1dc94f01

Author: emonty

test-requirements.txt

@@ -4,8 +4,6 @@ pyflakes==0.7.2
 flake8==2.0
 hacking>=0.5.3,<0.6
 
-distribute>=0.6.24
-
 coverage
 discover
 fixtures>=0.3.12