fork: Remove upstream branding

[bazaah]

Unclear around what the trademark/copyright situation is, but regardless it would be wrong for us to use other people's branding for our projects.

We should think about ensuring technical commits are always separate from ones around the social / repo stuff, so that we can easily cherry-pick commits into a branch we can contribute back.

[bazaah]

decided on adding the trailer X-Should-Upstream, which should be set to a falsey value (no/0/false) on commits we're not going to upstream