Remove Traffic Ops APIv2

[ocket8888]

This Improvement request (usability, performance, tech debt, etc.) affects these Traffic Control components:

• Traffic Ops

Current behavior:

The deprecated Traffic Ops API version 2 exists.

New behavior:

The deprecated Traffic Ops API version 2 no longer exists.

This includes, but is not necessarily limited to

• The API v2 Go client github.com/apache/trafficcontrol/traffic_ops/v2-client
• APIv2 support in the Python client
• APIv2 documentation
• APIv2 routes in the github.com/apache/trafficcontrol/traffic_ops/traffic_ops_golang/routing package
• Route handlers and "CRUDer" data structures in github.com/apache/trafficcontrol/traffic_ops/traffic_ops_golang and sub-packages thereof that are specific to APIv2
• Data structures in github.com/apache/trafficcontrol/lib/go-tc that are specific to API v2

[zrhoffman]

Closed in #6945