Fix T84517: Two geometry node trees added with "New" button

Adding the modifier itself already adds a new node tree, which is
then displayed in the node editor because of the active object and
active modifier context. So there's no need to create the node tree
in the python code in this case.

release/scripts/startup/bl_operators/geometry_nodes.py

@@ -62,9 +62,6 @@ class NewGeometryNodesModifier(bpy.types.Operator):
         if not modifier:
             return {'CANCELLED'}
 
-        group = geometry_node_group_empty_new(context)
-        modifier.node_group = group
-
         return {'FINISHED'}