Don't generate empty doc sections and reduce code duplication

doc/classes/InputEventMouseButton.xml

@@ -9,8 +9,6 @@
 	<tutorials>
 		<link title="Mouse and input coordinates">https://docs.godotengine.org/en/latest/tutorials/inputs/mouse_and_input_coordinates.html</link>
 	</tutorials>
-	<methods>
-	</methods>
 	<members>
 		<member name="button_index" type="int" setter="set_button_index" getter="get_button_index" enum="MouseButton" default="0">
 			The mouse button identifier, one of the [enum MouseButton] button or button wheel constants.
@@ -25,6 +23,4 @@
 			If [code]true[/code], the mouse button's state is pressed. If [code]false[/code], the mouse button's state is released.
 		</member>
 	</members>
-	<constants>
-	</constants>
 </class>