We're removing ruby193-v8 (it's not ruby193-rubygem-v8). You can also see there is no libv8, only ruby193-v8, in the channel if you filter on v8: https://rhn.redhat.com/rhn/channels/PackageList.do?cid=18330

There also isn't listed a rubygem-v8 listed as a dependency on rubygems.org: http://rubygems.org/gems/libv8