ReplicationTasksStorage: Remove synchronized from list* methods

These synchronized statements were added to make the tests pass.
However, they have undesirable behavior when considering production
systems (such as the concern raised in [1]).

[1] https://gerrit-review.googlesource.com/c/plugins/replication/+/280357/comment/757c5227_0de2800d/

Change-Id: I5556ea318aed400eb43c60fdbda41106dd4a17ff

src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationTasksStorage.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationTasksStorage.java b/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationTasksStorage.java
index 048767f..ee470cc 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationTasksStorage.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationTasksStorage.java
@@ -132,11 +132,11 @@
     }
   }
 
-  public synchronized List<ReplicateRefUpdate> listWaiting() {
+  public List<ReplicateRefUpdate> listWaiting() {
     return list(createDir(waitingUpdates));
   }
 
-  public synchronized List<ReplicateRefUpdate> listRunning() {
+  public List<ReplicateRefUpdate> listRunning() {
     return list(createDir(runningUpdates));
   }