[ldapfeed] use LDAP_SCOPES to find user-scope We already have LDAP_SCOPES dict defining possible scopes, this avoid possible code injection from config... Thus we can drop global variables already defined in LDAP_SCOPES since they are not used directly anymore.

Tests: skeleton-packaging
Depends:
 python-cubicweb, cubicweb-ctl,
 python-pyramid, python-wsgicors,
 devscripts, equivs, lintian, autopkgtest
Restrictions: allow-stderr, needs-root