TinyMCE: Deleted visitor groups should be displayed on a red background

Description

When a deleted visitor group is present in TinyMCE, it is missing the red background that indicates that the visitor group no longer exists.

Steps to reproduce

1. Create a visitor group.
2. Use the TinyMCE editor to personalize content and add the newly created visitor group.
3. Note the visitor group is displayed with a styled gray background.
4. Delete the newly-created visitor group.
5. Go back to the content that was personalized.

Expected:
The visitor group name should be displayed on a red background.

Actual:
The visitor group name is displayed as text with no background.