Migrate all itests to the new test kit (kit2)

[raulk]

Migrate all itests to the new test kit introduced in #6329. Take the opportunity to simplify the tests and tidy them up.

• batch_deal_test.go refactor batch deal test to use kit2 #6486
• ccupgrade_test.go Refactor ccupgrade test to use kit2 #6470
• cli_test.go Refactor cli test to kit2 #6464
• deadlines_test.go Refactor deadline toggling test to kit2 #6511
• gateway_test.go convert multisig and gateway tests to kit2 #6483
• multisig_test.go convert multisig and gateway tests to kit2 #6483
• paych_api_test.go convert paych tests to kit2 #6467
• paych_cli_test.go refactor paych cli tests to use kit2 #6484
• sdr_upgrade_test.go Refactor itest sdr upgrade #6488
• sector_pledge_test.go Refactor sector pledge test to use kit2 #6506
• sector_terminate_test.go refactor sector terminate test to use kit2 #6507
• tape_test.go Refactor tape test to kit2 #6468
• verifreg_test.go Refactor verifreg test to kit2 #6469
• wdpost_dispute_test.go Refactor test wdpost dispute test to use kit2 #6510
• wdpost_test.go refactor: wdpost test to kit2 #6509