remove cbtop from project repository

now it has separate repo within couchbaselabs account:
    https://github.com/couchbaselabs/cbtop

Change-Id: I76de7e72b0040aa0780b0e6f5f992b6c65797d65
Reviewed-on: http://review.couchbase.org/24676
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Ronnie Sun <ronnie@couchbase.com>