Remove unused test-requirments

WebOb is not needed in our test code.
So remove it to make less dependences.

Change-Id: I4910263449ff3d49c4ee44a6ef7a7762875fe76f

Author: chenchaozhe1988

test-requirements.txt

@@ -15,7 +15,6 @@ sphinx!=1.2.0,!=1.3b1,<1.3,>=1.1.2 # BSD
 os-testr>=0.4.1 # Apache-2.0
 testrepository>=0.0.18 # Apache-2.0/BSD
 testtools>=1.4.0 # MIT
-WebOb>=1.2.3 # MIT
 tempest-lib>=0.14.0 # Apache-2.0
 
 # Install these to generate sphinx autodocs