Don't set HOMEBREW_BUILD_BOTTLE.

This stops Homebrew's bottles from ever being used and `post_install`
blocks from being run when Homebrew is run by Boxen. If Boxen
maintainers want to build bottles they can/should manually set this
variable themselves.

Author: MikeMcQuaid

lib/puppet/provider/package/homebrew.rb

@@ -189,7 +189,6 @@ def command_opts
         "PATH"                      => "#{self.class.home}/bin:/usr/bin:/usr/sbin:/bin:/sbin",
         "BOXEN_HOMEBREW_BOTTLE_URL" => bottle_url,
         "HOMEBREW_CACHE"            => self.class.cache,
-        "HOMEBREW_BUILD_BOTTLE"     => "1"
       },
       :failonfail         => true,
       :uid                => default_user