Remove support for combining SARIF runs with non-unique categories #4395

Job	Run time
Diagnostic export (macos-latest, nightly-latest)	1m 36s
Diagnostic export (macos-latest, linked)	1m 15s
Diagnostic export (ubuntu-latest, nightly-latest)	1m 5s
Diagnostic export (windows-latest, nightly-latest)	5m 15s
Diagnostic export (ubuntu-latest, linked)	1m 5s
Diagnostic export (windows-latest, linked)	4m 30s
	14m 46s

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