RFC: Remove implicit field creation

[sloria]

Proposal: Remove Implicit/inferred field creation (fields and additional class Meta options).

At the very least, it's an unnecessary feature that adds complexity to the codebase. At worst, it interacts in weird ways with consuming libraries that autogenerate fields (see #923). The feature was added pre-1.0, when there were no ORM integration libs, as a poor man's ModelSerializer. At this point, though, I think we can remove it.

[MikeBadescu]

To clarify, do you still plan to keep the Schema class meta unknown?

    class Meta:
        unknown = INCLUDE

[sloria]

Yes, the unknown field API will remain the unchanged.

[MikeBadescu]

Thank you!

[sloria]

Let's consider this accepted for 4.0.

[lafrech]

Achieved in #2705.