Deprecate use of postMergeBannerTranslation

[Paul Wackerow]

Issue

The "post merge banner" and logic/strings surrounding it are no longer needed.

Currently the postMergeBannerTranslation front matter property is only being used on one page (in all languages), public/content/governance/index.md (/governance/ path). This file uses the Static layout, which does not actually handle this variable.

Meanwhile, we do handle it in the Tutorial layout, but no tutorials have this property anymore.

Scope

Beta Give feedback

1. Remove all postMergeBannerTranslation properties from the front matter of the governance pages
2. Remove logic surrounding use of postMergeBannerTranslationString in the Tutorial.tsx layout, and remove use of PostMergeBanner component
3. Deprecate/remove Banners/PostMergeBanner.tsx component
4. Remove the "page-upgrades-post-merge-banner-governance-ood" string from page-upgrades.json for all languages

[Colin McKerracher]

I'd like to take this on if that's alright!

[Paul Wackerow]

Great, thanks @colmck, assigned you