May deprecated `Seq.filter`?

[way-zer]

This function is confusing. In many language, the filter don't modify itself.
And the kotlin has Iterable<T>.filter that is very confusing with the Seq.filter, this two has different effect.

For some usecauses, like Vars.contents.blocks.filter() will make game boom. While Groups.player.filter is very useful and safe to use.

To deprecated

1. mark Seq.filter as deprecated.(no binrary breakchange)
2. use Seq.removeAll replace almost usecase.

[Anuken]

Was deprecated.