Also don't make it so windows can never shrink

That was misguided... I think an artefact of bad MultiWindow code that was in earlier

container/innerwindow.go

@@ -97,7 +97,6 @@ var _ fyne.WidgetRenderer = (*innerWindowRenderer)(nil)
 
 type innerWindowRenderer struct {
 	*intWidget.ShadowingRenderer
-	min fyne.Size
 
 	win           *InnerWindow
 	bar           *fyne.Container
@@ -135,9 +134,6 @@ func (i *innerWindowRenderer) MinSize() fyne.Size {
 	contentMin := i.win.content.MinSize()
 	barMin := i.bar.MinSize()
 
-	// only allow windows to grow, as per normal windows
-	contentMin = contentMin.Max(i.min)
-	i.min = contentMin
 	innerWidth := fyne.Max(barMin.Width, contentMin.Width)
 
 	return fyne.NewSize(innerWidth+pad*2, contentMin.Height+pad+barMin.Height).Add(fyne.NewSquareSize(pad))