Change Ldap SDK License to LGPL-2.1 (#45116)

We currently use the unboundid ldap SDK, which is triply licensed under
GPL-2.0, LGPL-2.1, and the "UnboundID LDAP SDK Free Use License". We currently
identify the license as the latter, but LGPL-2.1 is the one we should be using
per our policy.

Author: tomcallahan