core/state: rename Delete/IsDeleted to Suicide/HasSuicided

The delete/remove naming has caused endless confusion in the past.

core/vm/environment.go

@@ -105,9 +105,12 @@ type Database interface {
 	GetState(common.Address, common.Hash) common.Hash
 	SetState(common.Address, common.Hash, common.Hash)
 
-	Delete(common.Address) bool
+	Suicide(common.Address) bool
+	HasSuicided(common.Address) bool
+
+	// Exist reports whether the given account exists in state.
+	// Notably this should also return true for suicided accounts.
 	Exist(common.Address) bool
-	IsDeleted(common.Address) bool
 }
 
 // Account represents a contract or basic ethereum account.