Revert "ui/app: make window event queue buffered"

Breaks the ack mechanism of sending a dummy ack event to ensure
the previous event has been processed.

This reverts commit 7582b835bc.

ui/app/window.go

@@ -86,9 +86,8 @@ func NewWindow(opts *WindowOptions) *Window {
 	}
 
 	w := &Window{
-		in: make(chan Event),
-		// Make room for buffered input events.
-		out:         make(chan Event, 100),
+		in:          make(chan Event),
+		out:         make(chan Event),
 		ack:         make(chan struct{}),
 		invalidates: make(chan struct{}, 1),
 		frames:      make(chan *ui.Ops),