LanguageModuleRequirement: remove rbx support

This test wasn't running by default, so we missed that it wasn't
actually being executed - or that it was failing when running in the
testing environment.

As far as I can tell this is not, and has not, been used either in core
or in any tap, third party or otherwise, so just remove the feature and
its test.

Library/Homebrew/dependency_collector.rb

@@ -18,7 +18,7 @@ require "set"
 class DependencyCollector
   # Define the languages that we can handle as external dependencies.
   LANGUAGE_MODULES = Set[
-    :chicken, :jruby, :lua, :node, :ocaml, :perl, :python, :python3, :rbx, :ruby
+    :chicken, :jruby, :lua, :node, :ocaml, :perl, :python, :python3, :ruby
   ].freeze
 
   CACHE = {}

Library/Homebrew/requirements/language_module_requirement.rb

@@ -31,7 +31,6 @@ class LanguageModuleRequirement < Requirement
     when :python then %W[/usr/bin/env python -c import\ #{@import_name}]
     when :python3 then %W[/usr/bin/env python3 -c import\ #{@import_name}]
     when :ruby then %W[/usr/bin/env ruby -rubygems -e require\ '#{@import_name}']
-    when :rbx then %W[/usr/bin/env rbx -rubygems -e require\ '#{@import_name}']
     end
   end
 
@@ -46,7 +45,6 @@ class LanguageModuleRequirement < Requirement
     when :perl    then "cpan -i"
     when :python  then "pip install"
     when :python3 then "pip3 install"
-    when :rbx     then "rbx gem install"
     when :ruby    then "gem install"
     end
   end

Library/Homebrew/test/test_language_module_requirement.rb

@@ -51,16 +51,6 @@ class LanguageModuleRequirementTests < Homebrew::TestCase
     assert_deps_pass "date" => :ruby
   end
 
-  if which("rbx")
-    def test_bad_rubinius_deps
-      assert_deps_fail "notapackage" => :rbx
-    end
-
-    def test_good_rubinius_deps
-      assert_deps_pass "date" => :rbx
-    end
-  end
-
   if which("csc")
     def test_bad_chicken_deps
       assert_deps_fail "notapackage" => :chicken