This environment variable allows telling Homebrew to use the `SUDO_USER`
variable to `sudo` through that user when Homebrew (Cask) attempts to
run `sudo`.
While we're here, clarify in some messaging that we're running `sudo`
and that that's the password we're asking for; the specific password is
configuration dependent and not the specific password for the user.
Similarly, remove the `Package installers may write to any location`
output; it's kinda spammy and doesn't feel like the right place.
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