[AI-FSSDK] [FSSDK-12368] Remove legacy flag-level holdout fields #1558

Job	Run time
typescript_test	1m 29s
browser_tests (firefox)	8m 51s
unit_tests (24)	1m 27s
unit_tests (18)	1m 32s
browser_tests (safari)	3m 22s
unit_tests (22)	1m 25s
fullstack_production_suite / test	6s
browser_tests (chrome)	7m 17s
browser_tests (edge)	6m 41s
unit_tests (20)	1m 32s
lint	54s
lint_markdown_files / lint	1m 8s
integration_tests / test	7s
Coveralls coverage	4s
	35m 55s

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