refactor(ui): drop quicksettings companion machinery for secondary unet

The secondary unet loads from the networks panel toggle or the settings
page; companion ordering and dynamic visibility pushes in ui_settings.py
are not worth their footprint for one setting.

modules/shared_items.py

@@ -116,12 +116,6 @@ def refresh_unet_list():
     modules.sd_unet.refresh_unet_list()
 
 
-def sd_unet_secondary_visible():
-    import modules.sd_unet
-    from modules import shared
-    return shared.sd_model_type in modules.sd_unet.DUAL_TRANSFORMER_TYPES
-
-
 def sd_te_items():
     import modules.model_te
     predefined = ['Default']