- As discussed in
https://github.com/Homebrew/brew/pull/14976#issuecomment-1474544569
and further comments, this is needed because in order to enforce the
order of `on_{arch,system}` blocks we need to have everything
consistently within one of those blocks.
- We previously allowed overrides where the top-level `version` stanza
would be the default, unless on an OS that had an `on_system` block
with a `version` specified. But this breaks down when we try to order
the `on_system` blocks because if a `url` at the top-level has a
`version` interpolated in it, then the `version` stanza needs to be
above the `url` stanza. But it could be that `version` is OS-specific.
- Let's stop allowing overrides and require that everything be in an
`on_system` block. This will make it easier to enforce the order of
`on_system` blocks in a future PR (14976).
