[ci] cannot CI couchbase, requires libcouchbase

requirements/test-ci.txt

@@ -2,7 +2,6 @@ coverage>=3.0
 coveralls
 -r extras/redis.txt
 -r extras/cassandra.txt
--r extras/couchbase.txt
 -r extras/mongodb.txt
 -r extras/riak.txt
 -r extras/sqlalchemy.txt