Remove non-Pydantic connection request handling code

[sajith]

If/when #149 is merged, we probably should not keep the old code around. These all could go:

• sdx_datamodel.models.connection.py
• sdx_datamodel.models.connection_qos_metrics.py
• sdx_datamodel.models.connection_qos_unit.py
• sdx_datamodel.models.connection_scheduling.py
• sdx_datamodel.models.connection_v2.py
• sdx_datamodel.validation.connectionvalidator.py

We could re-purpose the tests where possible.