remove unneded readme for a shared db dir

docker/templates/db_data_readme.md

-# TARGET: docker/containers/db-server/var_tmp_db-data/readme.txt
-
-# Info
-
-content of `docker/containers/db_server/var_tmp_db-data/` will be visible in the database container as `/var/tmp/db-data/`. It is a helper to transfer/ import sqldumps.