Enable ruby-macho by default.

Flips HOMEBREW_RUBY_MACHO to HOMEBREW_NO_RUBY_MACHO.

Library/Homebrew/dev-cmd/test-bot.rb

@@ -909,7 +909,6 @@ module Homebrew
 
     ENV["HOMEBREW_DEVELOPER"] = "1"
     ENV["HOMEBREW_SANDBOX"] = "1"
-    ENV["HOMEBREW_RUBY_MACHO"] = "1"
     ENV["HOMEBREW_NO_EMOJI"] = "1"
     ENV["HOMEBREW_FAIL_LOG_LINES"] = "150"
     ENV["HOMEBREW_EXPERIMENTAL_FILTER_FLAGS_ON_DEPS"] = "1"

Library/Homebrew/os/mac/keg.rb

@@ -1,5 +1,5 @@
 class Keg
-  if ENV["HOMEBREW_RUBY_MACHO"]
+  if !ENV["HOMEBREW_NO_RUBY_MACHO"]
     require "os/mac/ruby_keg"
     include RubyKeg
   else

Library/Homebrew/os/mac/pathname.rb

@@ -1,7 +1,7 @@
 require "os/mac/shared_mach"
 
 class Pathname
-  if ENV["HOMEBREW_RUBY_MACHO"]
+  if !ENV["HOMEBREW_NO_RUBY_MACHO"]
     require "os/mac/ruby_mach"
     include RubyMachO
   else