[DAC] Remove legacy mode

Depends on #4613 (closed).

Once operating modes are supported by the DAC node, support for the Legacy mode should be dropped

• Refactor all integration tests to use the full dac infrastructure
  1. !9340 (merged) remove all the legacy specific tests
  2. !9346 (merged) migrate the Legacy module tests to Full_infrastructure
  3. !9348 (merged) migrate the Legacy.Signature_manager module tests to Full_infrastructure.Signature_manager
• !9349 (merged) remove the Legacy operating mode