Fix stale plugin docs and dead links

- unraid_api.php comment still told you to run Deployment/deploy.sh,
  deleted a while back
- VaraverkSettings.page linked to a CHANGELOG.md that doesn't exist
  anywhere in the repo
- Manual-Plugin.md / README-Plugin.md described manually heredoc-ing the
  .plg locally and a .txz-based install that isn't wired up — rewritten
  to describe the actual install flow (raw .plg URL via Plugins ->
  Install Plugin), with plugin_setup.sh's dev-symlink role called out
  separately from that install path

Plugin/unraid/VaraverkSettings.page

@@ -30,9 +30,4 @@ _(Scripts directory)_:
      style="color:#555;text-decoration:none;">
     Issues
   </a>
-  &nbsp;·&nbsp;
-  <a href="https://github.com/FailedProxy/Varaverk/blob/main/CHANGELOG.md" target="_blank"
-     style="color:#555;text-decoration:none;">
-    Changelog
-  </a>
 </div>