Drop support for Node < v14.14 and remove rimraf dependency

[mansona]

I was hoping to be able to fix this without having to do a major release but it looks like we're backed into a corner 😞

The e18e project suggests the removal of rimraf after Node v14.14 https://e18e.dev/docs/replacements/rimraf.html and if we were to update to the next major of rimraf (to remove the deprecation) then we would need to only support Node v14 anyway: https://github.com/isaacs/rimraf/blob/main/CHANGELOG.md#v40

So to remove the deprecation we need to do a major and we might as well target at least Node v14.14 to remove the dependency 👍

[kategengler]

I am fine with this but I also argue we should drop all the Nodes not currently supported by ember-cli and ember.js and modernize further:

This will need to be a major so users of this package will need to update their deps anyway and it will not be able to float back to older versions of ember-cli and other packages in the default blueprint.