🔨 clean: remove unused code

[lucasrodes]

• Remove chart revision v1 code.
• Move indicator_upgrade logic to a dedicated module.

In months time: remove all chart-revision code (inc. v2)

[owidbot]

Quick links (staging server): Site	Admin	Wizard

Login: ssh owid@staging-site-remove-stuff

chart-diff: ✅

No charts for review.

data-diff: ✅ No differences found

```diff Legend: +New ~Modified -Removed =Identical Details Hint: Run this locally with etl diff REMOTE data/ --include yourdataset --verbose --snippet ``` Automatically updated datasets matching _weekly_wildfires|excess_mortality|covid|fluid|flunet|country_profile|garden/ihme_gbd/2019/gbd_risk_ are not included

Edited: 2024-06-11 09:21:04 UTC Execution time: 32.47 seconds