Dealloc first time RCTNetInfo reachability callback

Summary:
@public
We're seeing a crasher where `self` on line 54 isn't an `RCTNetInfo`. The timing looks related to D9798488, so my theory is that this class is being deallocated before it resolves, and thus causes a crash.

Reviewed By: PeteTheHeat

Differential Revision: D10127341

fbshipit-source-id: 94eaba7def6b118092adcf6b4cce841ccc7d0b59

Libraries/Network/RCTNetInfo.m

@@ -105,6 +105,14 @@ - (void)stopObserving
   }
 }
 
+- (void)dealloc
+{
+  if (_firstTimeReachability) {
+    SCNetworkReachabilityUnscheduleFromRunLoop(self->_firstTimeReachability, CFRunLoopGetMain(), kCFRunLoopCommonModes);
+    CFRelease(self->_firstTimeReachability);
+  }
+}
+
 - (SCNetworkReachabilityRef)getReachabilityRef
 {
   SCNetworkReachabilityRef reachability = SCNetworkReachabilityCreateWithName(kCFAllocatorDefault, _host.UTF8String ?: "apple.com");