I've found the internal `without_transaction_enrollment` callbacks which
have not been newly used over five years, when I tried to work reverting
#9068 (https://github.com/rails/rails/pull/36049#issuecomment-487318060).

I think that we will never make that callbacks public, since the
mechanism of `without_transaction_enrollment` is too implementation
specific, at least before #9068, records in a transaction had enrolled
all into the transaction.

That callbacks was introduced at #18936 to make `touch_later` #19324,
but I think that the internal callbacks is overkill to just make the
`touch_later` only, and invoking the extra callbacks also have a little
overhead even if we haven't used that.

So I think we can remove the internal callbacks for now, until we will
come up with a good use for that callbacks.