use debians packaged cargo, should be fresh enough these days

Dockerfile_debian

@@ -16,15 +16,11 @@ RUN apt-get update \
        git-core \
        make \
        llvm \
+       cargo \
        build-essential \
        openssh-client \
        libssl-dev zlib1g-dev libbz2-dev libreadline-dev libsqlite3-dev wget \
        libncurses5-dev xz-utils tk-dev libxml2-dev libxmlsec1-dev libffi-dev liblzma-dev \
-    # No recent enough Rust in Debian packages (2021-02-11)
-    && curl -o /tmp/rustup.sh --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs \
-    && chmod +x /tmp/rustup.sh \
-    && /tmp/rustup.sh -y \
-    && echo 'source /root/.cargo/env' >> /root/.profile \
     # githublab ssh
     && mkdir -p -m 0700 ~/.ssh && ssh-keyscan gitlab.com github.com | sort > ~/.ssh/known_hosts \
     # install pyenv