Remove goja type assertion

The remote parser no longer works with goja so the result from evaluate
will not return a goja value. Now just type assert without goja.

common/screenshotter.go

@@ -278,7 +278,6 @@ func (s *screenshotter) screenshotElement(h *ElementHandle, opts *ElementHandleS
 	}
 
 	documentRect := bbox
-	rt := h.execCtx.vu.Runtime()
 	scrollOffset := h.Evaluate(`() => { return {x: window.scrollX, y: window.scrollY};}`)
 
 	var returnVal Position