Don't build the dock tile plug-in: it's too flaky.

- Sometimes unexpectedly displays (the wrong color) on top of Shroud when it's running, though app drawing should take precedence.
- Bundle stays open, prohibiting ejecting of the disk image, even if you don't choose to keep Shroud in the Dock.
- Would have to kill com.apple.dock.extra or SystemUIServer to handle updates.