Drop ldap support (Closes #124)

- this was included in the original version of Go before cas
was fully utilised
- I'm not sure it even works and has been sitting around for a long time
- will slightly speed up builds
4 jobs for 124-drop-ldap-support in 1 minute and 29 seconds (queued for 3 seconds)
Status Name Job ID Coverage
  Test
passed Go-py2.7 #1588

00:00:47

passed Go-py3.4 #1589

00:01:28

passed Go-py3.5 #1590

00:01:28

passed Go-py3.6 #1591

00:01:28

56.0%