remove some unneeded plugin manager calls #1744

Job	Run time
e2e_tests (latest, 7.2)	16m 50s
unit_tests (latest, 7.2, singlesite)	8m 29s
checkstyle	20s
e2e_tests (latest, 8.1)	4m 12s
unit_tests (latest, 7.2, multisite)	9m 3s
e2e_tests (trunk, 7.2)	17m 13s
unit_tests (latest, 8.1, singlesite)	8m 41s
e2e_tests (trunk, 8.1)	17m 21s
unit_tests (latest, 8.1, multisite)	8m 51s
unit_tests (5.2, 7.2, singlesite)	9m 12s
unit_tests (5.2, 7.2, multisite)	9m 15s
	1h 49m 27s

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