Remove `disable_combine_sarif_files` feature flag #4564

Job	Run time
Config export (ubuntu-latest, nightly-latest)	1m 21s
Config export (ubuntu-latest, linked)	1m 0s
Config export (windows-latest, linked)	1m 48s
Config export (macos-latest, linked)	1m 34s
Config export (windows-latest, nightly-latest)	3m 11s
Config export (macos-latest, nightly-latest)	2m 18s
	11m 12s

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