AbstractSubcriber: Fix FloggerFormatString pattern flagged by error prone

Build is failing with recent Error Prone version:

  AbstractSubcriber.java:79: error: [FloggerFormatString]
  missing argument for format specifier '%s'
        logger.atSevere().withCause(e).log(
                                          ^
    (see https://errorprone.info/bugpattern/FloggerFormatString)

Change-Id: I254a4c78f80feaab6f92eae306a7a2047ecccbd1
diff --git a/src/main/java/com/googlesource/gerrit/plugins/multisite/consumer/AbstractSubcriber.java b/src/main/java/com/googlesource/gerrit/plugins/multisite/consumer/AbstractSubcriber.java
index 816edc9..1f8766a 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/multisite/consumer/AbstractSubcriber.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/multisite/consumer/AbstractSubcriber.java
@@ -76,12 +76,10 @@
         subscriberMetrics.incrementSubscriberConsumedMessage();
         subscriberMetrics.updateReplicationStatusMetrics(event);
       } catch (IOException e) {
-        logger.atSevere().withCause(e).log(
-            "Malformed event '%s': [Exception: %s]", event.getHeader());
+        logger.atSevere().withCause(e).log("Malformed event '%s'", event.getHeader());
         subscriberMetrics.incrementSubscriberFailedToConsumeMessage();
       } catch (PermissionBackendException | CacheNotFoundException e) {
-        logger.atSevere().withCause(e).log(
-            "Cannot handle message %s: [Exception: %s]", event.getHeader());
+        logger.atSevere().withCause(e).log("Cannot handle message '%s'", event.getHeader());
         subscriberMetrics.incrementSubscriberFailedToConsumeMessage();
       }
     }