According to [Codesearch](https://codesearch.wmcloud.org/search/?q=growthsetmentorweight&i=nope&files=&excludeFiles=&repos=), `action=growthsetmentorweight` is not used by GrowthExperiments code (or other MW code). Instead, `action=options` is used by the weight changing JS. With the switch to the structured mentor list (T264343), this API will no longer work (instead, `action=growthmanagementorlist` will have to be used). Since it appears to be unused, removing it looks like the best option.
==== Places to check before removing
[ ] Check callers of the API (can be done using `event.mediawiki_api_request` in Hadoop, or `api.log` at `mwlog1002`
[ ] Check user scripts (`mwgrep` at mwmaint1002)
==== Acceptance criteria
[ ] The `action=growthsetmentorweight` API is no longer available