Fix: remove UI code relating to bone layers

Since #109976 was merged, one would run into the following when opening
Bone Relations panel in Properties:

```
/build_linux/bin/4.0/scripts/startup/bl_ui/properties_data_bone.py:228
rna_uiItemR: property not found: Bone.layers
```

So now remove the UI code there (since Bone.layers are no more...)

Pull Request: https://projects.blender.org/blender/blender/pulls/111730

scripts/startup/bl_ui/properties_data_bone.py

@@ -224,12 +224,6 @@ class BONE_PT_relations(BoneButtonsPanel, Panel):
             bone = context.edit_bone
 
         col = layout.column()
-        col.use_property_split = False
-        col.prop(bone, "layers", text="")
-        col.use_property_split = True
-        col = layout.column()
-
-        col.separator()
 
         if context.bone:
             col.prop(bone, "parent")