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 <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Roman Klauke <[email protected]>