Removing ipython from edx dependencies.

Ipython is not strictly required to run edx-platform. It can
be setup as part of Vagrant provision scripts, or manually
by each developer as required in specific cases.

requirements/edx/base.txt

@@ -76,9 +76,6 @@ xmltodict==0.4.1
 django-ratelimit-backend==0.6
 unicodecsv==0.9.4
 
-# Used for debugging
-ipython==0.13.1
-
 # Used for development operation
 watchdog==0.6.0