Request #4676 has been accepted by arcanis [1]:
Merged heroku-toolbelt and heroku-client to heroku-client-standalone
instead.
The first ones installs to /usr/local which is not recommended. In
other hand heroku-client-standalone installs to /opt, which is more
pretty for standalone applications.
Also heroku-client-standalone has the newest version.
[1] https://aur.archlinux.org/account/arcanis/