Remove RawJSON

Nobody has claimed this yet.

This was vital pre Go 1.8 but since then things have changed:

> A [RawMessage](https://go.dev/pkg/encoding/json/#RawMessage) value now marshals the same as its pointer type.

https://go.dev/doc/go1.8

So the example failure in this comment actually works fine in newer Go versions:
```
// RawJSON is a reimplementation of json.RawMessage that supports being used as a value type
//
// For example:
//
// jsonBytes, _ := json.Marshal(struct{
// RawMessage json.RawMessage
// RawJSON RawJSON
// }{
// json.RawMessage(`"Hello"`),
// RawJSON(`"World"`),
// })
//
// Results in:
//
// {"RawMessage":"IkhlbGxvIg==","RawJSON":"World"}
//
// See https://play.golang.org/p/FzhKIJP8-I for a full example.
type RawJSON []byte
```

Search the repository for the RawJSON type, its references, and the comment example, then read the surrounding Go code. Remove the obsolete type and update any affected references or documentation; the work is done when the project’s Go tests pass and no RawJSON references remain.

Written by the indexing model from the issue text.