2.2.0: massive bundle size increase

**Describe the bug**
The bundle size for `2.2.0-beta` almost doubles compared to `2.1.3`.

ember-cli-bundle-analyzer lists the following sizes added to vendor.js
`5.4kb` version `2.1.3`
`10.3kb` version `2.2.0-beta`

I think this is due to bundling the modifier version together with the non modifier version, even though both code paths are pretty much independent from each other.

For the `2.2.0` release it would be great if either both versions could be released separately, or the non-modifier version would be dropped in favour of the modifier version (which would also mean old ember versions would no longer be able to use the latest version of ember-sortable).

Keeping the current way of packaging would lead to unnecessary bloat of consuming ember apps, as always both versions of this addon will be included and will have to be parsed and compiled by the browser, which easily leads to performance issues especially on mobile.