bin/uglifyjs should be implemented solely with the minify() API

There are too many implementation inconsistencies between the CLI and `minify()`. Uglify should [eat its own dog food](https://en.wikipedia.org/wiki/Eating_your_own_dog_food). This will decrease the maintenance burden long term and lead to a better `minify()` API.

See: https://github.com/mishoo/UglifyJS2/pull/1274#issuecomment-244496866
