[multi-sources-removal] Simplify repo.delete_info_multi arguments, uri is no more used Related to #2919300

[multi-sources-removal] Drop deleted_entities system table and entities.mtime column since they were only used by the entities_modified_since api of the repository which has been dropped. Along with them, the multi-sources-etypes configuration variable and some sql queries at modification/deletion time of entities. Bon vent ! Related to #2919300

[multi-sources-removal] drop repository entities_modified_since public api actually only used by pyrorql/zmqrql sources which have been dropped. This will allow to drop a bunch of system meta-data (eg deleted_entities) Related to #2919300