Cleanup - feature gate of `stop_sibling_instruction_search_at_parent` #6111

Job	Run time
test	0s
cargo-test-sbf (token/program)	9m 10s
cargo-test-sbf (instruction-padding/program, token/program-2022, token/program-2022-test)	15m 36s
check	0s
cargo-test-sbf (associated-token-account/program, associated-token-account/program-test)	10m 14s
cargo-test-sbf (token-upgrade/program)	9m 15s
cargo-test-sbf (feature-proposal/program)	9m 18s
cargo-test-sbf (governance/addin-mock/program, governance/program)	12m 36s
cargo-test-sbf (memo/program)	8m 46s
cargo-test-sbf (name-service/program)	8m 57s
cargo-test-sbf (stake-pool/program)	12m 18s
cargo-test-sbf (single-pool/program)	9m 47s
	1h 45m 57s

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