MINOR: Stop staging LICENSE/NOTICE into kafka-site content dir (#23906)

Follow-up to KAFKA-21289 (#23833), which fixed `release.py stage-docs`
for the Hugo-based kafka-site layout.

The site-docs tar carries the repo's top-level `LICENSE` and `NOTICE` at
its root. `stage-docs` extracts the tar with `tar xf ...
--strip-components 1` straight into `content/en/<version>/`, so those
two files get dumped into the  kafka-site content tree alongside the
actual docs. They are not docs content and do not belong there — the
previous release slot (`content/en/43`) has neither, and the javadoc
tree already carries its own `legal/` license files under
`static/<version>/javadoc/`.

This was flagged on the 4.4 kafka-site PR, where `content/en/44/LICENSE`
and `content/en/44/NOTICE` showed up as spurious additions and had to be
removed by hand. Without this change they return on every `stage-docs`
run.

This patch drops `LICENSE` and `NOTICE` from the content directory after
extraction, mirroring the existing post-extraction cleanup that moves
`images/` out to `static/<version>/`.

No behavior change for any other staged file.

Reviewers: Chia-Ping Tsai <chia7712@gmail.com>

release/release.py

@@ -162,6 +162,14 @@ def command_stage_docs():
         static_images_path = os.path.join(static_docs_path, "images")
         cmd("Moving images to static assets", f"mkdir -p {static_images_path} && cp -R {content_images_path}/. {static_images_path} && rm -rf {content_images_path}", shell=True)
 
+    # LICENSE and NOTICE sit at the root of the site-docs tar and get dumped into
+    # content/en/<version> by the extract above, but they are not docs content and
+    # do not belong in the kafka-site content tree. Drop them after extraction.
+    for stray_file in ("LICENSE", "NOTICE"):
+        stray_path = os.path.join(content_docs_path, stray_file)
+        if os.path.exists(stray_path):
+            cmd(f"Removing stray {stray_file}", f"rm -f {stray_path}")
+
     javadocs_src_dir = os.path.join(repo_dir, "build", "docs", "javadoc")
 
     cmd("Copying javadocs", f"cp -R {javadocs_src_dir} {static_docs_path}")