Revert "Documented has_and_belongs_to_many relationships."

This reverts commit 6d23b0cbc7384383a2ebc5f8f0ab0867c8259abf.
Documented has_and_belongs_to_many relationships.

- There was a lack of documentation for how to create factories with
models that have has_and_belongs_to_many relationships.
- An example is provided to show how to accomplish this.
- This functionality was already present, this is only a documentation
update.

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