Hide --no-system from uv pip tree CLI (#9040)

## Summary

This is hidden from all other commands, so it looks like an oversight.

Closes #9035.

docs/reference/cli.md

@@ -7033,7 +7033,7 @@ uv pip tree [OPTIONS]
 <p>May also be set with the <code>UV_NO_PROGRESS</code> environment variable.</p>
 </dd><dt><code>--no-python-downloads</code></dt><dd><p>Disable automatic downloads of Python.</p>
 
-</dd><dt><code>--no-system</code></dt><dt><code>--offline</code></dt><dd><p>Disable network access.</p>
+</dd><dt><code>--offline</code></dt><dd><p>Disable network access.</p>
 
 <p>When disabled, uv will only use locally cached data and locally available files.</p>