"test_has_offline_migrations_pending_contract_scripts" is testing a
non supported branch, "Kilo". The usefulness expired when this branch
was declared EOL.
"test_has_offline_migrations_all_heads_upgraded" is tested in
"test_forbid_offline_migrations_starting_newton". Since "Newton",
no more DB contract migrations are allowed. Both tests are checking
the same behavior.
Due to the time extension and the lack of value of those tests, this
patch removes both.