disabling fastboot asset generation

[ghost]

After adding ember-fetch, I now see a dist/ember-fetch/fetch-fastboot.js generated after each build. I would like to disable this functionality as we do not use fastboot in our application.
Is this possible?
If not, and we can agree it is worthwhile, I can help with a PR.

[xg-wang]

I think the generation can detect ember-cli-fastboot because the file is only used by fastboot.

[xg-wang]

https://github.com/ember-cli/ember-fetch/releases/tag/v7.1.0 won't generate fastboot asset if ember-cli-fasboot isn't installed or skipped by env flag