After recent changes allowing ThreadItems to have IDs, they can now
also have warnings about duplicate IDs.
Bug: T267035
Change-Id: If3edfe34e6e29741e29fac8946a3c88badc4ab7f
We avoided fixing these because it causes changes in just about all of
the test data, which is annoying when reviewing or blaming changes.
But the previous several commits also caused changes in just about all
of the test data, so we might as well do this too.
Change-Id: I83b64d83b6f12c04dc06c0cadff7cdd89417e137