This counts how many times the remote peer has told this Phase-1 tunnel to tear down a Phase-2 (IPsec) SA, per its description. It's a signal of tunnel churn or intentional traffic-selector changes on the peer's side, since each delete request means an active data SA is being torn down and will likely need renegotiation. A steady trickle of one or two per day may be normal rekey-related housekeeping, but a burst of dozens within minutes suggests the peer is flapping or was just reconfigured.