[multi-sources-removal] drop source location search on glob_*[entity|relation] methods
source is now always the system source
Related to #2919300
[jcr: fix wrong rebase in symmetric relation removal]
usr/lib/PY_VERSION/*-packages/cubicweb/server/
usr/lib/PY_VERSION/*-packages/cubicweb/hooks/
usr/lib/PY_VERSION/*-packages/cubicweb/sobjects/
usr/lib/PY_VERSION/*-packages/cubicweb/schemas/
usr/share/cubicweb/migration/