MB-7849:  don't delete the ctypes directory, just the ctypes-1... dir

Change-Id: I7d4c11d8f41aabaa8bb384d54009424945654562
Reviewed-on: http://review.couchbase.org/26338
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>