tools: remove obsolete lint config file

All JS files have been moved out of the `src` directory so the
`.eslintrc` file in that directory can also be removed.

PR-URL: #5959
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Roman Klauke <romankl@users.noreply.github.com>