misc: don't use 'required' qml keyword

Support Qt versions less than 5.15. This is not a good idea.
Something is wrong with package deployment.

Change-Id: Idc3daef154f7994f8e5ca089a3a0c6fe4d97dacf

src/commoncomponents/PhotoboothView.qml

@@ -31,7 +31,7 @@ Item {
 
     property bool isPreviewing: false
     property alias imageId: avatar.imageId
-    required property real avatarSize
+    property real avatarSize
 
     signal focusOnPreviousItem
     signal focusOnNextItem