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 Job ID Name Coverage
  Test
passed #1588
Go-py2.7

00:00:47

passed #1589
Go-py3.4

00:01:28

passed #1590
Go-py3.5

00:01:28

passed #1591
Go-py3.6

00:01:28

56.0%