[Dashboard] Rewrite/remove add_histograms_queue TODOs
[Dashboard] Rewrite/remove add_histograms_queue TODOs

I rewrote TODOs that mentioned bugs to mention them directly, and removed a
bunch of TODOs that have to do with speculative refactoring/optimization.

TBR=d3ffe0e065c2328e497bb32a07f4dcb29138ef5b@chromium.org

Change-Id: I0c55429162171f195e5d0fec8338afbf886ac565
Reviewed-on: https://chromium-review.googlesource.com/c/1297603
Reviewed-by: Ethan Kuefner <b3258c73b307e35b2725bc68d7434c38b3a2b146@chromium.org>
Reviewed-by: Ben Hayden <d3ffe0e065c2328e497bb32a07f4dcb29138ef5b@chromium.org>
Commit-Queue: Ethan Kuefner <b3258c73b307e35b2725bc68d7434c38b3a2b146@chromium.org>

catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult