Investigate removing activity gated callbacks

The idea of activity gated callbacks was created to mitigate callbacks getting events not made for them now that the callbacks are always running. However, both @DominicOram and @dperl-dls dislike them:

* @DominicOram thinks that having both the activity flag in the metadata and checking the run name in the start document means that ones redundant
* @dperl-dls thinks they make it confusing when we have callbacks that are chained from other callbacks
* Both dislike the extra layer in general

## Acceptance Criteria
* Remove the activity gate
* Make sure in every callback when we get a start/event we have a check like `if doc.get("subplan_name") == CONST.PLAN.ROTATION_OUTER:` to make sure we're only doing something on the expected events
* Make sure in the stops we match them to the start we care about and teardown anything that needs cleaning up
* Make `subplan_name` a constant
* Document this pattern and reasoning behind it - send this to core as an FYI