The advertised default is that anything in share/info is removed unless
the user sets HOMEBREW_KEEP_INFO, but we've actually been installing the
files *unless* the variable is set. To illustrate:
$ unset HOMEBREW_KEEP_INFO
$ brew install -v wdiff
[...]
ln /usr/local/share/locale/af/LC_MESSAGES/wdiff-gnulib.mo
ln /usr/local/share/info/wdiff.info
ln /usr/local/share/info/dir
==> Summary
[...]
$ HOMEBREW_KEEP_INFO=1 brew install -v wdiff
ln /usr/local/share/locale/af/LC_MESSAGES/wdiff-gnulib.mo
==> Summary
[...]
Obviously not what we wanted.
ClosesHomebrew/homebrew#7989.
Signed-off-by: Jack Nagel <jacknagel@gmail.com>