[FSSDK-12080] remove holdouts feature toggle (#1110) #1403

Job	Run time
lint	1m 30s
unit_tests (18)	1m 58s
unit_tests (24)	1m 41s
lint_markdown_files / lint	1m 9s
unit_tests (20)	1m 59s
unit_tests (22)	1m 59s
fullstack_production_suite / test	7s
integration_tests / test	6s
Coveralls coverage	0s
	10m 29s

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