Drop Mozilla LDAP SDK detection, update --with-ldap code

[yadij]

Mozilla has not maintained their LDAP SDK since 2017: https://wiki.mozilla.org/LDAP_C_SDK#Latest_News_-_10.2F13.2F2017

Admin needing to use that SDK can ./configure Squid with:

--with-ldap=/path/to/sdk CPPFLAGS=-I/path/to/sdk/mozldap