[BUG]ConcurrentModificationException when finish transaction

[wangbo]

Describe the bug

2020-12-01 21:53:59,216 WARN 37 [PublishVersionDaemon.publishVersion():210] finish ts 1046352935 failed 
java.util.ConcurrentModificationException: null
        at java.util.HashMap$HashIterator.nextNode(HashMap.java:1490) ~[?:?]
        at java.util.HashMap$ValueIterator.next(HashMap.java:1518) ~[?:?]
        at org.apache.doris.transaction.GlobalTransactionMgr.finishTransaction(GlobalTransactionMgr.java:700) ~[palo-fe.jar:?]
        at org.apache.doris.transaction.PublishVersionDaemon.publishVersion(PublishVersionDaemon.java:208) [palo-fe.jar:?]
        at org.apache.doris.transaction.PublishVersionDaemon.runAfterCatalogReady(PublishVersionDaemon.java:55) [palo-fe.jar:?]
        at org.apache.doris.common.util.MasterDaemon.runOneCycle(MasterDaemon.java:58) [palo-fe.jar:?]

Doris version: 0.12
but 0.13 also has the same problem
The reason is it doesn't use correct method to remove a element from a collection when iterating the collection