Don't store the agda path in the config

[ncfavier]

When switching between projects that use different versions of Agda, I have to clear the agda path and restart vscode every time, which is annoying.

If there is a use case for saving the path in the config, we could expose this as a setting. Or maybe only save when the path is not empty.

I couldn't build rescript on NixOS so I didn't regenerate the javascript.

[ncfavier]

My current workaround for this is to set the Agda path to a shell script that just does exec agda "$@".

[banacorn]

Thanks!

[ncfavier]

Don't forget to rebuild the JS!