[source] Drop source mapping handling
It was only used by the cwxmlparser which has been deleted. This is too complex
for litle benefit, we don't want to maintain that in cubicweb.
# Check the CW versions and add the entity only if needed ?
add_entity_type('CWSession')
rql('DELETE CWProperty X WHERE X pkey "system.version.pyramid"',
ask_confirm=False)
sql('DROP TABLE moved_entities')
sql('ALTER TABLE entities DROP COLUMN asource')
sql('ALTER TABLE entities DROP COLUMN extid')
drop_entity_type('CWSourceSchemaConfig')