Cleanup Rubinius workaround

features/command_line/warnings_option.feature

@@ -2,7 +2,6 @@ Feature: `--warnings` option (run with warnings enabled)
 
   You can use the `--warnings` option to run specs with warnings enabled
 
-  @unsupported-on-rbx
   Scenario:
     Given a file named "example_spec.rb" with:
       """ruby
@@ -15,7 +14,6 @@ Feature: `--warnings` option (run with warnings enabled)
     When I run `rspec --warnings example_spec.rb`
     Then the output should contain "warning"
 
-  @unsupported-on-rbx
   Scenario:
     Given a file named "example_spec.rb" with:
       """ruby

features/core_standalone.feature

@@ -5,8 +5,6 @@ Feature: Use rspec-core without rspec-mocks or rspec-expectations
   available, but rspec-core can be used just fine without either of those
   gems installed.
 
-  # Rubinius stacktrace includes kernel/loader.rb etc.
-  @unsupported-on-rbx
   Scenario: Use only rspec-core when only it is installed
     Given only rspec-core is installed
       And a file named "core_only_spec.rb" with: