[tests/querier] use the new connection api (part 3/3)
Some adaptations to devtools/repotest:
* dead code removal
* remove session related code
In the tests:
* many tests actually don't check the querier but some generic rql
property -- when such a test needs several statements to complete a
commit, switch to session.new_cnx
* provide an assertRQLEqual helper
sync_schema_props_perms('cw_source', syncprops=False)
if schema['BigInt'].eid is None:
add_entity_type('BigInt')