Homebrew developers have the corresponding variable permanently set in
their environment and wanting to appear like a Homebrew developer for a
single invocation is exceedingly rare. Additionally, the option won't be
recognized by `bin/brew`. (It is also undocumented.)
Using `HOMEBREW_DEVELOPER=1 brew <command>` is still possible, and not
more inconvenient than passing the `--homebrew-developer` option.
ClosesHomebrew/homebrew#48322.
Signed-off-by: Martin Afanasjew <martin@afanasjew.de>