remove redundant volatile (sofastack#329)

* perf: remove redundant volatile

* fix: leaderInfo should be use volatile

* fix: recover these variables are use volatile that the get method is not protect by synchronized.

* fix: the get method of pushedVersion and attributes is not protect by synchronized when in print log.

server/store/api/src/main/java/com/alipay/sofa/registry/store/api/elector/AbstractLeaderElector.java

@@ -41,7 +41,7 @@ public abstract class AbstractLeaderElector implements LeaderElector {
 
   private volatile boolean startElector = false;
 
-  private volatile boolean isObserver = false;
+  private boolean isObserver = false;
 
   private final LeaderElectorTrigger leaderElectorTrigger = new LeaderElectorTrigger();