Fix: Allow uncoloring Vue Nodes (#5991)

## Summary

Fixes an issue where trying to uncolor a node broke the vue color
syncing.

## Changes

- **What**: Changes litegraph property removal from `delete` to `=
undefined`

## Screenshots

### Before 


https://github.com/user-attachments/assets/81a1ad40-ba5d-4dec-8f90-5b61eb804a16

### After


https://github.com/user-attachments/assets/459d2d15-c728-49d2-abd9-6e255e5383e5

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-5991-Fix-Allow-uncoloring-Vue-Nodes-2876d73d365081f4a74fc9fa423aae1c)
by [Unito](https://www.unito.io)

tests-ui/tests/litegraph/core/LGraphNodeProperties.test.ts

@@ -46,12 +46,12 @@ describe('LGraphNodeProperties', () => {
       })
     })
 
-    it("should not emit events when value doesn't change", () => {
+    it('should emit event when value is set to the same value', () => {
       new LGraphNodeProperties(mockNode)
 
       mockNode.title = 'Test Node' // Same value as original
 
-      expect(mockGraph.trigger).toHaveBeenCalledTimes(0)
+      expect(mockGraph.trigger).toHaveBeenCalledTimes(1)
     })
 
     it('should not emit events when node has no graph', () => {