An 'x' ("Remove USS selector from this element") button displayed on example selectors when root USS is selected

Steps to reproduce:

1. Create and open a new project
2. Create and open a new USS file in Window -> UI Toolkit -> UI Builder
3. Select the root .uss element in the StyleSheets section of UI Builder
4. Observe the UI Builder's Inspector

Actual results: 'x' buttons are displayed next to each example selector

Expected results: No 'x' button is displayed next to the example selectors

Reproducible with versions: 6000.6.0a6

Not reproducible with versions: 6000.0.76f1, 6000.3.16f1, 6000.4.9f1, 6000.5.0b10, 6000.6.0a5

Tested on (OS): Windows 11 Pro (25H2)

Notes:

• The buttons are non-functional