Companion to https://github.com/Homebrew/brew/pull/7698.
Provide better, `odeprecated` messaging for
`depends_on :macos => :mavericks` and otherwise just fix up the code
that relied on `:mavericks`.
We're not actually using this anywhere and it makes the code
more complicated.
Relatedly, this PR fixes the issue where
`uses_from_macos "python@2" => :build` was valid on macOS but not
on Linux.
