These should be done after we fully move to 2-stage promotion

README.md 

• 2 mentions of /preview in "Environments and Deployments" section
• Also remove any references to 'Candidate' branch!

MR templates

• The release-candidate template can be removed as there will be no candidate release; from staging directly to production!
• Also update the GA-release template to remove references to candidate

External docs

• Update Promotion Manager Duties to remove references to Candidate branch in text and diagrams!

• Update Picking order Script Doc' remove references to Candidate branch in text