### Description
We recently completed work to break out the Math API into its own spec, hosted through wikimedia.org instead of the standard per-wiki path. Although the module was renamed correctly, there are additional areas that require clean up for clarity within the Sandbox experience.
### Conditions of acceptance
[x] Update 'Math' header --> it currently reads "Wikimedia REST API" which is in conflict with the actual Wikimedia REST API. It should instead read "Math API".
[x] Update initial description for the Math API for accuracy --> Halley will help review and suggest changes.
[x] Update stability policy to read as "deprecated" for the deprecated per-wiki Math endpoints --> https://www.mediawiki.org/wiki/API_versioning#Deprecated
[x] Remove `/page/data-parsoid` endpoint from the per-wiki specs. --> See: https://phabricator.wikimedia.org/T393557