core/state: make TestSnapshotRandom work again (#3816)

In `touch` operation, only `touched` filed has been changed. Therefore
in the related undo function, only `touched` field should be reverted.
In addition, whether remove this obj from dirty map should depend on
prevDirty flag.

core/state/statedb_test.go

@@ -116,7 +116,6 @@ func TestIntermediateLeaks(t *testing.T) {
 }
 
 func TestSnapshotRandom(t *testing.T) {
-	t.Skip("@fjl fix me please")
 	config := &quick.Config{MaxCount: 1000}
 	err := quick.Check((*snapshotTest).run, config)
 	if cerr, ok := err.(*quick.CheckError); ok {