docs(docker): remove stale Dockerfile.alpine comment (#2068)

Remove the "keep in sync with docker/Dockerfile.alpine" comment in
docker/Dockerfile: that file does not exist in the repo, so the comment
points at nothing.

Author: fengmk2

docker/Dockerfile

@@ -58,8 +58,6 @@ ENV VP_HOME=/home/vp/.vite-plus \
 # downloads its own pinned Node.js at build time, so the default is dead weight in a
 # builder image. The node/npm/npx shims remain and fetch the right version on
 # first use.
-#
-# Keep this install line in sync with docker/Dockerfile.alpine.
 RUN curl -fsSL https://vite.plus | VP_VERSION="${VP_VERSION}" VP_PR_VERSION="${VP_PR_VERSION}" bash \
  && vp --version \
  && rm -rf "$VP_HOME/js_runtime"