[Java] Remove singleton exceptions (#6765)

java/api/src/main/java/org/ray/api/exception/RayActorException.java

@@ -8,9 +8,8 @@ package org.ray.api.exception;
  */
 public class RayActorException extends RayException {
 
-  public static final RayActorException INSTANCE = new RayActorException();
-
-  private RayActorException() {
+  public RayActorException() {
     super("The actor died unexpectedly before finishing this task.");
   }
+
 }

java/api/src/main/java/org/ray/api/exception/RayWorkerException.java

@@ -5,9 +5,8 @@ package org.ray.api.exception;
  */
 public class RayWorkerException extends RayException {
 
-  public static final RayWorkerException INSTANCE = new RayWorkerException();
-
-  private RayWorkerException() {
+  public RayWorkerException() {
     super("The worker died unexpectedly while executing this task.");
   }
+
 }

java/runtime/src/main/java/org/ray/runtime/object/ObjectSerializer.java

@@ -45,9 +45,9 @@ public class ObjectSerializer {
       if (Arrays.equals(meta, RAW_TYPE_META)) {
         return data;
       } else if (Arrays.equals(meta, WORKER_EXCEPTION_META)) {
-        return RayWorkerException.INSTANCE;
+        return new RayWorkerException();
       } else if (Arrays.equals(meta, ACTOR_EXCEPTION_META)) {
-        return RayActorException.INSTANCE;
+        return new RayActorException();
       } else if (Arrays.equals(meta, UNRECONSTRUCTABLE_EXCEPTION_META)) {
         return new UnreconstructableException(objectId);
       } else if (Arrays.equals(meta, TASK_EXECUTION_EXCEPTION_META)) {