The class `TextSourceLabel` is unused, as is the associated factory method `TextLabelFactory.createSimple(...)`.

The abstractions provided by the abstract classes `TextLabel` and `ExtendedTextLabel` only make sense when there are two types of text labels (`TextSourceLabel` and `ExtendedTextSourceLabel`). With the deletion of `TextSourceLabel`, both `TextLabel` and `ExtendedTextLabel` can also be removed.

See initial mailing list discussion: https://mail.openjdk.org/pipermail/client-libs-dev/2025-September/032302.html