Remove support for combining SARIF runs with non-unique categories #4450

Job	Run time
Config export (windows-latest, linked)	3m 28s
Config export (macos-latest, linked)	1m 9s
Config export (ubuntu-latest, linked)	1m 2s
Config export (ubuntu-latest, nightly-latest)	1m 15s
Config export (windows-latest, nightly-latest)	2m 50s
Config export (macos-latest, nightly-latest)	1m 3s
	10m 47s

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