don't duplicate requirements

version of twisted is already specified in spring package

Change-Id: Id57660bca63cced9c2dd247eea32b318bd5c2e2e
Reviewed-on: http://review.couchbase.org/36683
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>