Remove nose support

[brettcannon]

Usage is extremely low and we are going to be rewriting our test support overall. We will not be removing support until it is necessary, though.

[tamaroth]

Well, this made me extremely sad. I have just lost the ability to debug my tests since they're all written with nosetests.

Is there a way around this other than rewriting tests (impossible) or regressing version of vscode to prior to this change (undesirable)?