[Catch-all] Fix broken Discourse link in GitBook header

[laurabelinfante]

Summary

The GitBook header includes a link to Discourse that's broken. The fix
is to either remove the broken link or replace it with a link to the
current community forum.

Acceptance criteria

• Broken Discourse link is removed from the GitBook header
• If a replacement community link belongs there, it points to the
  active forum

[SnowboardTechie]

@laurabelinfante it looks like I'll need create permission in the Gitbook app to do this.

[laurabelinfante]

@SnowboardTechie you were a creator, but I just made you an admin so you should be all set now.

[SnowboardTechie]

That did the trick, I've updated the link to be for the Forum -> https://forum.simpler.grants.gov