Fix bug in timer clean up

Summary:
One of the impacts of this bug is that Java is firing timer
completion events into JavaScript for timers that should have
been deleted. JavaScript filters these out so it doesn't impact
the app developer. However, Java is completing more timers
than necessary.

When cleaning up a timer, we were accidentally deleting the
whole set of timers for that context. Instead, we should
just delete that timer from its context.

Adam Comella
Microsoft Corp.
Closes #9361

Differential Revision: D3797573

fbshipit-source-id: c30ed600af741601f2babdfc61da9aac549cbadb

ReactAndroid/src/main/java/com/facebook/react/modules/core/Timing.java

@@ -104,7 +104,13 @@ public void doFrame(long frameTimeNanos) {
             timer.mTargetTime = frameTimeMillis + timer.mInterval;
             mTimers.add(timer);
           } else {
-            mTimerIdsToTimers.remove(timer.mExecutorToken);
+            SparseArray<Timer> timers = mTimerIdsToTimers.get(timer.mExecutorToken);
+            if (timers != null) {
+              timers.remove(timer.mCallbackID);
+              if (timers.size() == 0) {
+                mTimerIdsToTimers.remove(timer.mExecutorToken);
+              }
+            }
           }
         }
       }
@@ -385,7 +391,10 @@ public void deleteTimer(ExecutorToken executorToken, int timerId) {
         return;
       }
       // We may have already called/removed it
-      mTimerIdsToTimers.remove(executorToken);
+      timersForContext.remove(timerId);
+      if (timersForContext.size() == 0) {
+        mTimerIdsToTimers.remove(executorToken);
+      }
       mTimers.remove(timer);
     }
   }