How can I disable Skitch's "Discard Skitch Note" dialog when quitting?
This prompt has to do with Skitch's ability to upload/sync screenshots to Evernote. Because you don't have this configured, it's asking if you're sure you want to quit without having done this synchronization. 

To disable this behavior you can go under Skitch &rarr; Preferences and select the Sync tab and change the preferences so that Skitch will only do manual syncing to Evernote.

Before

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After

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