[AI-FSSDK] [FSSDK-12368] Remove legacy flag-level holdout fields #1549

Job	Run time
integration_tests / test	8s
typescript_test	1m 35s
browser_tests (firefox)	8m 15s
unit_tests (22)	1m 14s
browser_tests (edge)	7m 9s
unit_tests (20)	1m 27s
lint_markdown_files / lint	1m 9s
fullstack_production_suite / test	5s
browser_tests (safari)	4m 38s
unit_tests (24)	1m 18s
lint	1m 6s
browser_tests (chrome)	7m 32s
unit_tests (18)	1m 29s
Coveralls coverage	0s
	37m 5s

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