Revert "Have a global and thread local observer in QueryObserverHolder"

This reverts commit 141e30f.

geode-core/src/main/java/org/apache/geode/cache/query/internal/QueryObserverHolder.java

@@ -14,7 +14,6 @@
  */
 package org.apache.geode.cache.query.internal;
 
-
 import org.apache.geode.annotations.Immutable;
 import org.apache.geode.annotations.internal.MakeNotStatic;
 
@@ -46,53 +45,35 @@ public class QueryObserverHolder {
    */
   @Immutable
   private static final QueryObserver NO_OBSERVER = new QueryObserverAdapter();
-  /**
-   * The threadlocal current observer which will be notified of all query events.
-   */
-  private static final ThreadLocal<QueryObserver> _instance = new ThreadLocal<>();
-
   /**
    * The current observer which will be notified of all query events.
    */
   @MakeNotStatic
-  private static volatile QueryObserver _globalInstance = NO_OBSERVER;
+  private static ThreadLocal<QueryObserver> _instance = ThreadLocal.withInitial(() -> NO_OBSERVER);
 
   /**
    * Set the given observer to be notified of query events. Returns the current observer.
    */
   public static QueryObserver setInstance(QueryObserver observer) {
     Support.assertArg(observer != null, "setInstance expects a non-null argument!");
-    QueryObserver oldObserver;
-    if (_instance.get() != null) {
-      oldObserver = _instance.get();
-    } else {
-      oldObserver = _globalInstance;
-    }
+    QueryObserver oldObserver = _instance.get();
     _instance.set(observer);
-    _globalInstance = observer;
     return oldObserver;
   }
 
   public static boolean hasObserver() {
-    if (_instance.get() != null) {
-      return _instance.get() != NO_OBSERVER;
-    }
-    return _globalInstance != NO_OBSERVER;
+    return _instance.get() != NO_OBSERVER;
   }
 
   /** Return the current QueryObserver instance */
   public static QueryObserver getInstance() {
-    if (_instance.get() != null) {
-      return _instance.get();
-    }
-    return _globalInstance;
+    return _instance.get();
   }
 
   /**
    * Only for test purposes.
    */
   public static void reset() {
     _instance.set(NO_OBSERVER);
-    _globalInstance = NO_OBSERVER;
   }
 }