Remove Babel requirement

We do not need Babel for this repository, remove it.

Change-Id: Ie7745a7e5d8c8442d84ec172dfa000f61c53523b

requirements.txt

@@ -3,7 +3,6 @@
 # process, which may cause wedges in the gate later.
 
 pbr>=1.6 # Apache-2.0
-Babel>=2.3.4 # BSD
 iso8601>=0.1.11 # MIT
 lxml>=2.3 # BSD
 oslo.config>=3.14.0 # Apache-2.0