Add @DoNotStrip annotation to JavaTimerManager.deleteTimer()

Summary:
This method is being stripped in release builds because it's used directly from C++ and not referenced in Java. Adding `DoNotStrip` to prevent this.

Changelog: [Internal]

Reviewed By: PeteTheHeat, mdvacca

Differential Revision: D19708826

fbshipit-source-id: a572f0295ab3b49e5884d0a6c723d65e4bbc9226

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

@@ -345,6 +345,7 @@ public class JavaTimerManager {
     createTimer(callbackID, adjustedDuration, repeat);
   }
 
+  @DoNotStrip
   public void deleteTimer(int timerId) {
     synchronized (mTimerGuard) {
       Timer timer = mTimerIdsToTimers.get(timerId);
@@ -356,6 +357,7 @@ public class JavaTimerManager {
     }
   }
 
+  @DoNotStrip
   public void setSendIdleEvents(final boolean sendIdleEvents) {
     synchronized (mIdleCallbackGuard) {
       mSendIdleEvents = sendIdleEvents;