Remove `postinstall` scripts. #27663

Job	Run time
Core running from src / MacOS	2m 55s
Core running from build / Windows	4m 16s
Core running from src / Windows	8m 44s
Core running from build / Linux	2m 47s
Core running from src / Linux	2m 18s
Core running from build / MacOS	2m 46s
Slack Notifications	0s
Failed workflow tasks	0s
	23m 46s

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