Pulp

Rationale:

"_type" / "pulp_type" is a field that shows up on models using master-detail inheritance. However, there is no way to query these types generically. In order to query these types, you have to provide the app name and the type name, which are the two components of that field. Therefore it doesn't really provide the end user any valuable information.

This is probably a leftover relic from when the /content/ endpoint existed and returned content of all types.

Pulpcore still needs this information for various things, but, the user doesn't. Therefore we can remove it from the serializers.

"_type" / "pulp_type" is the only thing provided by MasterModelSerializer, so the whole thing can go. Everything inheriting from MasterModelSerializer can inherit from ModelSerializer instead.

https://github.com/pulp/pulpcore/blob/master/pulpcore/app/serializers/base.py#L81-L110