Move `derailed_benchmarks` gem to default group
Move `derailed_benchmarks` gem to default group

Some benchmarks of the gem require booting the app in `production`
environment.

mmkassem/gitlabhq,stoplightio/gitlabhq,stoplightio/gitlabhq,mmkassem/gitlabhq,mmkassem/gitlabhq,stoplightio/gitlabhq,stoplightio/gitlabhq,mmkassem/gitlabhq