Revert "Fix ContentObserver unregister issue"

This reverts commit 2df4e144a9. 
It was causing failures in packages/apps/DocumentsUI tests

Bug: 63638102
Bug: 63154326
Change-Id: I51fb54f705f58f159f4fcc30bfed41ababcba950

core/java/android/database/ContentObserver.java

@@ -193,11 +193,6 @@ public abstract class ContentObserver {
      */
     private void dispatchChange(boolean selfChange, Uri uri, int userId) {
         if (mHandler == null) {
-            synchronized (mLock) {
-                if (mTransport == null) {
-                    return;
-                }
-            }
             onChange(selfChange, uri, userId);
         } else {
             mHandler.post(new NotificationRunnable(selfChange, uri, userId));
@@ -218,11 +213,6 @@ public abstract class ContentObserver {
 
         @Override
         public void run() {
-            synchronized (mLock) {
-                if (mTransport == null) {
-                    return;
-                }
-            }
             ContentObserver.this.onChange(mSelfChange, mUri, mUserId);
         }
     }