Updated release prep gitlab templates

Merge Info

• Related Issues

  • none

• Backport Timeline

  • Immediate - patchsets for critical bug fixes or other major blocker (e.g. fixes for a 0-day exploit) OR patchsets with trivial changes which do not need testing (e.g. fixes for typos or fixes easily verified in a local developer build)
  • Next Minor Stable Release - patchset that needs to be verified in nightly before backport
  • Eventually - patchset that needs to be verified in alpha before backport
  • No Backport - patchset for the next major stable

• Issue Tracking

  • Link resolved issues with appropriate Release Prep issue for changelog generation

Change Description

Updated release-prep:

• removed now obsolete torbutton steps from stable
• updated push steps to merge since we're just in gitlab now
• updated rebase process to better match how I actually do it
• simplified the tor-browser manual update steps