Don't generate empty doc sections and reduce code duplication

doc/classes/ReferenceRect.xml

@@ -8,8 +8,6 @@
 	</description>
 	<tutorials>
 	</tutorials>
-	<methods>
-	</methods>
 	<members>
 		<member name="border_color" type="Color" setter="set_border_color" getter="get_border_color" default="Color(1, 0, 0, 1)">
 			Sets the border [Color] of the [ReferenceRect].
@@ -21,6 +19,4 @@
 			If set to [code]true[/code], the [ReferenceRect] will only be visible while in editor. Otherwise, [ReferenceRect] will be visible in game.
 		</member>
 	</members>
-	<constants>
-	</constants>
 </class>