fdo#70393: move openldap to a subdir of external

Change-Id: I0225484e976b5317c2ac5d5b50ade153425f22b0
Reviewed-on: https://gerrit.libreoffice.org/6546
Reviewed-by: David Tardon <dtardon@redhat.com>
Tested-by: David Tardon <dtardon@redhat.com>