Converted __init__ module initialisation to new pattern

Thanks to Dr. Sybren for the BCON25 presentation that tipped me off to the existence of `register_classes_factory`.

io_scene_psk_psa/psk/ui.py

@@ -23,6 +23,10 @@ class PSK_PT_material(Panel):
         col.prop(material.psk, 'mesh_triangle_bit_flags', expand=True, text='Flags')
 
 
-classes = (
+_classes = (
     PSK_PT_material,
 )
+
+from bpy.utils import register_classes_factory
+register, unregister = register_classes_factory(_classes)
+