Before this commit, returning `false` in an ActiveRecord `before_` callback
such as `before_create` would halt the callback chain.
After this commit, the behavior is deprecated: will still work until
the next release of Rails but will also display a deprecation warning.
The preferred way to halt a callback chain is to explicitly `throw(:abort)`.
Method `delete_all` should not be invoking callbacks and this
feature was deprecated in Rails 4.0. This is being removed.
`delete_all` will continue to honor the `:dependent` option. However
if `:dependent` value is `:destroy` then the default deletion
strategy for that collection will be applied.
User can also force a deletion strategy by passing parameter to
`delete_all`. For example you can do `@post.comments.delete_all(:nullify)`
