[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.
addressbook
basket
blog
book
calendar
comment
company
email
file
folder
i18ncontent
keyword
link
mailinglist
person
tag
timeseries
vcsfile