Remove Filter and Freeze wrappers

[frankmcsherry]

We have various trace wrappers, each of which imposes a bit of a tax on modifying things and act as constraints on how we can evolve things. The Filter and Freeze wrappers are to my understanding not used, and are hard to use (they provide a new type of trace/batch/cursor, which is hard to hide behind an abstraction).

This PR removes them, and leaves the remaining wrappers as roughly the timestamp modifying wrappers (enter, enter_at, and frontier) plus the rc wrapper which I think is less a wrapper and more just a standard tool.

[antiguru]

I don't mind removing some untested code! Easy enough to get it back.

[frankmcsherry]

Further pondering, and I'm feeling even better. The filter wrapper is something that shouldn't be too hard to implement in user logic, e.g. in your join closure look at the keys and values and nope out appropriately. It would be great if the trace did this for you, but there's a perf tax that comes with it, and it's just a weird space to try to be in (moving per-row logic around, from user code into arrangement spackle). The freeze wrapper is neat but I'd be baffled if anyone used it successfully.