Output hot module logics on demand

[xboy2012]

According to the webpack docs https://webpack.js.org/api/loaders/#thishot

we can know if HMR is enabled during COMPILE PHASE.

The current code increase unnecessary codes in production. ( Hot Module Reload is never enabled in production)

Hope this little change may help generating smaller output codes.

I also found that refs variable is never used, so it could be removed safely.