[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
\.svn
^build$
^dist$
\.pyc$
\.pyo$
\.bak$
\.old$
\~$
\#.*?\#$
\.swp$
^doc/book/en/apidoc$
\.old$
syntax: regexp
.*/data/database/.*\.sqlite
.*/data/database/.*\.config
.*/data/database/tmpdb.*
.*/data/ldapdb/.*
^doc/html/
^doc/doctrees/
^doc/book/en/devweb/js_api/