formula_support: deprecate more keg_only reasons.

It's unnecessary extra complexity to have versions that are keg-only on
some versions of macOS and not others.

Initially this was to only do so on old versions of OS X and Xcode but
the discussion in https://github.com/Homebrew/brew/pull/4081 meant that
it made more sense to remove them all.

Remove Xcode.installed? guards.

RuboCop 0.55.0.

It's safe since 600d58f4 when
MacOS::Xcode.version started returning `Version::NULL` where
appropriate.

Cask Refactoring

missing: exit nonzero if missing deps are found

audit: new formulae should not have a HEAD spec

Update `rubocop-cask` to 0.18.1.

Add missing `MacOS.release` deprecation.

cli_parser: Refactor required argument for flag to '='

docs/Analytics: note retention period.

Due to [GDPR](https://www.eugdpr.org) Google Analytics have added
[data retention controls](https://support.google.com/analytics/answer/7667196).

Let's set these so that we don't keep any anonymous user data any longer
than we need it.

compat/extend/string: fix odisabled return.

`odisabled` will still return for a formula in `.brew`. This means
`EOS.undent` returns `nil` and the formula cannot be parsed. Instead
return the actual string in this case to avoid e.g. patches blowing up
with `nil` strings.

Fixes #4049.

Fix Cask search not showing remote matches.

Make release-notes command work from any location

bottle: Use @args

mirror: Add missing import for cli_parser

Keg#replace_text_in_files: fix incorrect replace order

* specify repository location using `-C` option
* change `newest` to `latest` when talking about the latest tagged
commit

The order of the regexes in `Keg#replace_text_in_files` matters.
Otherwise, `/usr/local/Cellar` will be replaced to
`@@HOMEBREW_PREFIX@@/Cellar` instead of `@@HOMEBREW_CELLAR@@`.

Fixes Homebrew/homebrew-core#26043.