Move some non-ISO predicates [call/9, error/2, findall/4] out of builtins

[rotu]

Fix #2942

Note that call/9 is still expected to be available at runtime, this just removes the pre-bootstrap stub.

[rotu]

@mthom, @triska Here's a good example of a PR which I divided into commits for ease of review. I intend for this to be squash-merged, but it's not necessary.

Silly process questions when writing this:

1. How do I test this adequately? Is cargo test sufficient?
2. Should I be running some code formatter to e.g. reflow comments and long export lists?

[bakaq]

Yes, cargo test should run all tests. We don't have a Prolog formatter (yet), so there's nothing to do in that front. We do use cargo fmt though for the Rust code.