guides: update rust guide (#24386)

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## Description

The DHI static image has no adduser package, plus it already runs as a
nonroot user. Removed that section from the Dockerfile.

## Related issues or tickets

Closes #24362

## Reviews

<!-- Notes for reviewers here -->
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- [ ] Editorial review

Signed-off-by: Craig Osterhout <craig.osterhout@docker.com>

content/guides/rust/build-images.md

@@ -121,18 +121,6 @@ RUN --mount=type=bind,source=src,target=src \
 
 FROM dhi.io/static:20250419 AS final
 
-# Create a non-privileged user that the app will run under.
-ARG UID=10001
-RUN adduser \
-    --disabled-password \
-    --gecos "" \
-    --home "/nonexistent" \
-    --shell "/sbin/nologin" \
-    --no-create-home \
-    --uid "${UID}" \
-    appuser
-USER appuser
-
 # Copy the executable from the "build" stage.
 COPY --from=build /bin/server /bin/