remove unnecessary field `MantleRestore.status.pool` #866

Job	Run time
build (3Mi, full-backup)	26m 22s
build (3Mi, backup-failure)	33m 38s
build (3Mi, change-to-standalone)	20m 59s
build (3Mi, incr-backup)	30m 36s
build (3Mi, change-to-primary)	29m 44s
build (200Gi, various-transfer-part-size)	20m 38s
build (3Mi, !//)	35m 6s
build (10Mi, various-transfer-part-size)	24m 10s
build (3Mi, change-to-secondary)	24m 53s
	4h 6m 6s

Provide feedback