remove all backend code for stats

Created by: camdencheek

This has been experimental (and not enabled by default) for a long time, doesn't work consistently, and its functionality will be replaced by compute/notebooks. Additionally, removing it will speed up backend refactors.

ALSO, this brings the search_results.go file down to below 1000 lines, which is a big difference from a year ago.

Test plan

This just removes code.