[devtools] deprecate usage of sources file for test
This is old support which clutters the code and should no more be used.
As this is rarely used (if it is) and test only, it feels ok to drop support at
once without a deprecation phase.
usr/lib/python2*/*-packages/cubicweb/dataimport/
usr/lib/python2*/*-packages/cubicweb/server/
usr/lib/python2*/*-packages/cubicweb/hooks/
usr/lib/python2*/*-packages/cubicweb/sobjects/
usr/lib/python2*/*-packages/cubicweb/schemas/
usr/share/cubicweb/migration/