Release guide doesn't need "run manually" section

The release guide contains a section on how to do steps manually. This section mostly just duplicates the contents of build_release_candidate.sh, meaning a) it doesn't add much utility and b) it constantly has to be kept up-to-date with build_release_candidate.sh. I propose removing the section entirely and keeping build_release_candidate.sh as the source of truth for what needs to happen.