Remove all obsolete nested REST API serializers

[jeremystretch]

Proposed Changes

Remove all nested_serializers modules within each app, as these classes are no longer utilized.

Justification

The use of static nested API serializer classes (except where needed to resolve circular imports) was deprecated in NetBox v4.1 under #17143.

Impact

These serializers will no longer be available for use by plugins. They can be replaced by passing nested=True to a model's primary serializer. For example:

device = NestedDeviceSerializer()

can be replaced with

device = DeviceSerializer(nested=True)