Remove filter() sass function

[yurm04]

We need to deprecate the filter() function from our public sass API. It is no longer used in polaris-react and we no longer want to support this functionality in the system. Let's remove this function altogether.

Breaking change, stage for v8.0.0-major

👋 Thanks for opening your first issue. A contributor should give feedback soon. If you haven’t already, please check out the contributing guidelines.