[devtools] _orig_cnx does not exist any more (missing change)

[c-c schema] option to show single etype (closes #3404831)

[multi-sources-removal] Drop entities.source column Since we remove federated multi-sources support, the same value ('system') is always stored in this column and so could be removed. Also, cleanup repository caches and a few api where the very same useless information could be removed. Closes #2919300, at last [jcr: restore sanity check of etype against schema in checkintegrity.has_eid]

[repo] pylint cleanup, mainly of imports, with a bit of style

[multi-sources-removal] Drop no more used federated ('true') multi-sources related code Related to #2919300 (almost done!)

[multi-sources-removal] Turn ConnectionsSet into simpler ConnectionWrapper also, SqliteConnectionWrapper becomes a subclass. This is allowed since now ConnectionsSet responsability has been reduced to handling the system source only. This changeset also: * drops useless cnxset_set / check_connection api * deprecates former .source / .connection / container api but it renames neither the session's cnxset attribute, nor the related repository method. Related to #2919300

[multi-sources-removal] Drop cnxset_freed from source interface Though a hack is still needed when using sqlite Related to #2919300

[cnxset] add backwards compat for cnxset.source_cnxs It's used at least in a vcsfile migration script.

[multi-sources-removal] Simplify ConnectionsSet internal structures and public methods since it now handles a connection to the system source only Related to #2919300 [jcr: adjust 3.17.11 migration, fix a number of bugs in new ConnectionsSet implementation, fix source.{open,close}_source_connections]

[ldap] simplify connection handling since we deleted ldapuser source, we don't need anymore the get_connection and ConnectionWrapper stuff (that was used to put the ldap connection into the cnxset). Also, we should simply let connection errors propagate so this is properly reported to import logs.