[server] Drop update_config method of source
It does not make sense anymore to update the config of a source instance
(subclass of cubicweb.server.sources.AbstractSource) now that they are always
built from database information (CWSource). In datafeed and ldapfeed, we
move all code from "update_config" method in "init" method.
This changeset fixes LDAPFeedUserDeletionTC.test_a_filter_inactivate() failure
(unittest_ldapsource.py) introduces in previous changeset.
### Requirements for tests in various cubicweb/**/test directories. ###
## shared by several test folders
cubicweb-card
docutils
Twisted < 16.0.0
webtest
## cubicweb/test
Pygments
mock
#fyzz XXX pip install fails
cubicweb-file
cubicweb-localperms
cubicweb-tag
## cubicweb/devtools/test
flake8
## cubicweb/hooks/test
psycopg2
## cubicweb/pyramid/test
pyramid >= 1.5.0
waitress >= 0.8.9
wsgicors >= 0.3
pyramid_multiauth
## cubicweb/sobject/test
cubicweb-comment