Quit Fix

Uncommenting the GTK delete_event code appears to fix https://github.com/adobe/brackets/issues/4611

I tested on Arch Linux 64-bit, using the latest brackets-shell and brackets versions. 
probably not a good idea to call browser->GetHost() after calling browser->GetHost()->CloseBrowser().  This may crash in future versions since theoretically it should delete the "browser" pointer on close.