revert my change, caused other unit test failures

h2/src/main/org/h2/engine/Session.java

@@ -938,12 +938,13 @@ public class Session extends SessionWithState {
     private void cleanTempTables(boolean closeSession) {
         if (localTempTables != null && localTempTables.size() > 0) {
             synchronized (database) {
-                HashMap<String, Table> tempTables = localTempTables;
-                localTempTables = null;
-                for (Table table : tempTables.values()) {
+                Iterator<Table> it = localTempTables.values().iterator();
+                while (it.hasNext()) {
+                    Table table = it.next();
                     if (closeSession || table.getOnCommitDrop()) {
                         modificationId++;
                         table.setModified();
+                        it.remove();
                         table.removeChildrenAndResources(this);
                         if (closeSession) {
                             // need to commit, otherwise recovery might