fix pendingDeletedLedgers not remove ledger

Author: fanjianye

bookkeeper-server/src/main/java/org/apache/bookkeeper/bookie/storage/ldb/LedgerMetadataIndex.java

@@ -345,6 +345,7 @@ public void removeDeletedLedgers() throws IOException {
                 log.debug("Persisting deletes of ledgers {}", deletedLedgers);
             }
 
+            pendingDeletedLedgers.clear();
             ledgersDb.sync();
         } finally {
             key.recycle();