From reading https://github.com/orgs/Homebrew/discussions/3328: I
initially thought we should just change "Updated" to "Modified" when
appropriate. After conversation with Bo98, though, I thought more and
saw that we're already checking for outdated formulae here so, rather
than ever traverse through the formula history, look at the outdated
formula and list them unless we've set
`HOMEBREW_UPDATE_REPORT_ALL_FORMULAE` in which case we show the
modifications.
While we're here, also do a bit of reformatting and renaming to better
clarify intent.