refactor dockerfile: remove layer

Dockerfile

@@ -9,21 +9,19 @@ RUN apk add --no-cache \
         mariadb-client=$MARIADB_CLIENT_PACKAGE_VERSION \
         openssh-server=$OPENSSH_PACKAGE_VERSION \
         tini=$TINI_PACKAGE_VERSION \
-    && adduser -S "$USER" \
+    && adduser -S -s /tmp/mysqldump.sh "$USER" \
     && mkdir "$SSHD_HOST_KEYS_DIR" \
     && chown -c "$USER" "$SSHD_HOST_KEYS_DIR"
 VOLUME $SSHD_HOST_KEYS_DIR
 
 # RUN apk add --no-cache man openssh-doc=$OPENSSH_PACKAGE_VERSION
 
-COPY entrypoint.sh /
-ENTRYPOINT ["/sbin/tini", "--", "/entrypoint.sh"]
 COPY sshd_config /etc/ssh/sshd_config
 EXPOSE 2200/tcp
+
 ENV MYSQLDUMP_ARGS --help
-RUN chmod a=rx /entrypoint.sh \
-    && chmod a=r /etc/ssh/sshd_config \
-    && sed -i 's#^\(dump:.*\):/sbin/nologin$#\1:/tmp/mysqldump.sh#' /etc/passwd
+COPY entrypoint.sh /
+ENTRYPOINT ["/sbin/tini", "--", "/entrypoint.sh"]
 
 USER $USER
 CMD ["/usr/sbin/sshd", "-D", "-e"]