Warning fixed

Removed Unused Variable

Got these warnings when running Rails test cases 

```ruby


/Users/arunagw/checkouts/rails/bundle/ruby/1.9.1/gems/benchmark-ips-1.2.0/lib/benchmark/ips.rb:240: warning: assigned but unused variable - seconds
/Users/arunagw/checkouts/rails/bundle/ruby/1.9.1/gems/benchmark-ips-1.2.0/lib/benchmark/ips.rb:240: warning: assigned but unused variable - seconds
../Users/arunagw/checkouts/rails/bundle/ruby/1.9.1/gems/benchmark-ips-1.2.0/lib/benchmark/ips.rb:240: warning: assigned but unused variable - seconds
/Users/arunagw/checkouts/rails/bundle/ruby/1.9.1/gems/benchmark-ips-1.2.0/lib/benchmark/ips.rb:240: warning: assigned but unused variable - seconds
./Users/arunagw/checkouts/rails/bundle/ruby/1.9.1/gems/benchmark-ips-1.2.0/lib/benchmark/ips.rb:240: warning: assigned but unused variable - seconds
./Users/arunagw/checkouts/rails/bundle/ruby/1.9.1/gems/benchmark-ips-1.2.0/lib/benchmark/ips.rb:240: warning: assigned but unused variable - seconds



```