[AI-FSSDK] [FSSDK-12368] Remove legacy flag-level holdout fields #1557

Job	Run time
lint	54s
browser_tests (safari)	8m 27s
typescript_test	1m 28s
browser_tests (edge)	8m 4s
unit_tests (20)	1m 35s
browser_tests (chrome)	6m 39s
unit_tests (24)	1m 17s
integration_tests / test	8s
unit_tests (18)	1m 44s
unit_tests (22)	1m 29s
browser_tests (firefox)	7m 36s
lint_markdown_files / lint	1m 9s
fullstack_production_suite / test	6s
Coveralls coverage	4s
	40m 40s

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