In #33325, `deprecate_methods` is replaced from `prepend` to completely
emurated `alias_method_chain`, it exposed two internal methods
`xxx_with_deprecation` and `xxx_without_deprecation`.

After that, #34648 restored the `prepend` implementation, which doesn't
expose any internal methods, so we no longer be able to ensure to always
expose that internal methods.

As I said at https://github.com/rails/rails/pull/33325#issuecomment-409016725,
I think that internal methods exposed is not a specification but a
limitation when using `alias_method_chain`, there is no longer a reason
to follow that limitation.