Remove handling for multiple aria-invalid attributes (#18587)
Fixes #13321
Summary of the issue:
The aria-invalid spec never supported multiple attributes, however browsers temporarily supported them.
This support no longer exists in Chrome or Firefox.
As such tests and handling for multiple aria-invalid attributes should be removed
Description of user facing changes:
None (as browser support was dropped a long time ago)
Description of developer facing changes:
None
Description of development approach:
Remove test case, simplify handling
