Offer to clean out old dotnet installs

[maddymontaquila]

It would be amazing if after first setup it offers to clear out old dotnet installs (ie /usr/local/share/dotnet on mac) - I am tempted to just fully delete that folder but not sure if it's "safe", so if that IS safe it could just print that out as guidance, otherwise would love if it could "safely" clean for me!

[nagilson]

I like this suggestion, I assume we'd only do this in terminal or full replacement mode.

One issue is that we'd need to elevate to remove anything from that folder, (same for any platform) so the UX for doing this might be a bit clunky. On Mac I think this would likely require sudo.