benchmark/driver.rb had removed the cost for while loop in benchmark/bm_vm1_*.rb,
and benchmark_driver.gem can achieve the same thing with `loop_count`.

But unfortunately current benchmark_driver.gem can't solve it only for vm1_yield.yml...

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63893 b2dd03c8-39d4-4d8f-98ff-823fe69b080e