test_rubyoptions.rb: only one Bogus object

* test/ruby/test_rubyoptions.rb (test_segv_loaded_features): leave
  only one Bogus object in $LOADED_FEATURES.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43198 b2dd03c8-39d4-4d8f-98ff-823fe69b080e