Remove outdated demo project reference

The reference to a custom mouse cursor demo project provided is outdated. I believe it should be removed until there's an up-to-date working demo project for custom mouse cursor that can be shared.

tutorials/inputs/custom_mouse_cursor.rst

@@ -87,12 +87,6 @@ Create a Node and attach the following script.
     Check :ref:`Input.set_custom_mouse_cursor() <class_Input_method_set_custom_mouse_cursor>`'s
     documentation for more information on usage and platform-specific caveats.
 
-Demo project
-------------
-
-Find out more by studying this demo project:
-https://github.com/guilhermefelipecgs/custom_hardware_cursor
-
 Cursor list
 -----------