remove unnecessary field `MantleRestore.status.pool` (#186) #867

Job	Run time
build (3Mi, incr-backup)	32m 59s
build (3Mi, change-to-primary)	26m 39s
build (3Mi, backup-failure)	35m 43s
build (3Mi, full-backup)	25m 47s
build (3Mi, change-to-secondary)	25m 44s
build (3Mi, change-to-standalone)	21m 55s
build (3Mi, !//)	41m 28s
build (10Mi, various-transfer-part-size)	21m 27s
build (200Gi, various-transfer-part-size)	20m 25s
	4h 12m 7s

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