LDAP: refactor use of "1.1" OID

I've noticed several people asking questions about the arbitrary usage
of ['1.1'] in code review, so I figured I'd refactor them into a
constant so it's a bit more self-documenting, since it's definition is,
in fact, completely arbitrary:

    If the client does not want any attributes returned, it can specify
    a list containing only the attribute with OID "1.1". This OID was
    chosen arbitrarily and does not correspond to any attribute in use.

Source: http://www.alvestrand.no/objectid/1.1.html

Change-Id: Ib2901bd8593b5a6ea8b6a5488f0d45b51fa8b77c
Merge "LDAP: refactor use of "1.1" OID"