Update docs for --publish-url to avoid duplication. (#8561)

## Summary

These two sentences in the docs for `--publish-url` seem to basically be
duplicates:


https://github.com/astral-sh/uv/blob/3eda248ef5678fe07b5424fb4f256011800fbb15/crates/uv-cli/src/lib.rs#L4616-L4618

I found the first to be easier to read, so this commit removes the
second.

## Test Plan

No tests, change is docs-only.

---------

Co-authored-by: Zanie Blue <contact@zanie.dev>

crates/uv-cli/src/lib.rs

@@ -4614,8 +4614,6 @@ pub struct PublishArgs {
     /// and index upload.
     ///
     /// Defaults to PyPI's publish URL (<https://upload.pypi.org/legacy/>).
-    ///
-    /// The default value is publish URL for PyPI (<https://upload.pypi.org/legacy/>).
     #[arg(long, env = EnvVars::UV_PUBLISH_URL)]
     pub publish_url: Option<Url>,