message: [cli] Remove broken `vc downgrade` command
  It maps to an "upgrade" command, which does not exist.
  Fixes:
  ```
  $ vc downgrade
  Vercel CLI 23.1.2
  Error! Cannot find module './upgrade'
  ```
diff: @@ -10,7 +10,6 @@ export default new Map([
  ['dns', 'dns'],
  ['domain', 'domains'],
  ['domains', 'domains'],
  - ['downgrade', 'upgrade'],
  ['env', 'env'],
  ['help', 'help'],
  ['init', 'init'],
  