fix(RadialMenu): remove unused image

The radial menu prefab had an unused image in it which has been
removed.

Assets/VRTK/Prefabs/RadialMenu.prefab

@@ -9,7 +9,6 @@ GameObject:
   m_Component:
   - component: {fileID: 22453742}
   - component: {fileID: 22297788}
-  - component: {fileID: 11469702}
   - component: {fileID: 11411068}
   - component: {fileID: 11446826}
   m_Layer: 5
@@ -207,33 +206,6 @@ MonoBehaviour:
   m_Name: 
   m_EditorClassIdentifier: 
   events: {fileID: 0}
---- !u!114 &11469702
-MonoBehaviour:
-  m_ObjectHideFlags: 1
-  m_PrefabParentObject: {fileID: 0}
-  m_PrefabInternal: {fileID: 100100000}
-  m_GameObject: {fileID: 122840}
-  m_Enabled: 0
-  m_EditorHideFlags: 0
-  m_Script: {fileID: -765806418, guid: f5f67c52d1564df4a8936ccd202a3bd8, type: 3}
-  m_Name: 
-  m_EditorClassIdentifier: 
-  m_Material: {fileID: 0}
-  m_Color: {r: 1, g: 1, b: 1, a: 0.392}
-  m_RaycastTarget: 1
-  m_OnCullStateChanged:
-    m_PersistentCalls:
-      m_Calls: []
-    m_TypeName: UnityEngine.UI.MaskableGraphic+CullStateChangedEvent, UnityEngine.UI,
-      Version=1.0.0.0, Culture=neutral, PublicKeyToken=null
-  m_Sprite: {fileID: 10907, guid: 0000000000000000f000000000000000, type: 0}
-  m_Type: 1
-  m_PreserveAspect: 0
-  m_FillCenter: 1
-  m_FillMethod: 4
-  m_FillAmount: 1
-  m_FillClockwise: 1
-  m_FillOrigin: 0
 --- !u!222 &22297788
 CanvasRenderer:
   m_ObjectHideFlags: 1