build(packaging): drop in-tree Homebrew formula (tap is canonical)

The homebrew-tap repo is now the canonical home for the formula (with
its own audit + release-bump automation), so remove packaging/homebrew/
to avoid a second source of truth. This empties packaging/ entirely:
all distribution packaging now lives in its external repo (pkgbuilds for
Arch, homebrew-tap for Homebrew). install.sh stays at the root.

Author: m-wells