Small clean-up for `EnsureForParachain` stuff #15304

Job	Run time
preflight / preflight	43s
preflight / ci-versions	59s
check-runtime-migration (westend)	7m 48s
check-runtime-migration (asset-hub-westend)	5m 45s
check-runtime-migration (bridge-hub-westend)	4m 59s
check-runtime-migration (collectives-westend)	5m 0s
check-runtime-migration (coretime-westend)	5m 13s
All runtime migrations passed	1s
	30m 28s

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