docs: drop the generated gt reference

The per-command reference made the pages long and repeated what
gt <command> --help shows. Keep the guides and remove the generator,
its workflow and the sidebar handling it needed.

Signed-off-by: bircni <[email protected]>

cli-sidebars.js

@@ -12,10 +12,5 @@ module.exports = {
     'authentication',
     'ci',
     'scripting',
-    {
-      type: 'category',
-      label: 'Reference',
-      items: [{ type: 'autogenerated', dirName: 'reference' }],
-    },
   ],
 };