Fix regression in force mouse selection

Shift+left click is means to force terminal selection and not passthrough
any mouse events, even if a mouse mode is enabled. The change this is
reverting from #4583 caused this feature to break by always installing a
global listener on Terminal.element so the SelectionService never got a
chance to cancel is.

Fixes #4781

src/browser/Terminal.ts

@@ -729,10 +729,8 @@ export class Terminal extends CoreTerminal implements ITerminal {
 
       if (!(events & CoreMouseEventType.UP)) {
         this._document!.removeEventListener('mouseup', requestedEvents.mouseup!);
-        el.removeEventListener('mouseup', requestedEvents.mouseup!);
         requestedEvents.mouseup = null;
       } else if (!requestedEvents.mouseup) {
-        el.addEventListener('mouseup', eventListeners.mouseup);
         requestedEvents.mouseup = eventListeners.mouseup;
       }