Fix: NetInfo.isConnected for iOS

Properly tear down the reachabilityRef in RCTNetInfo

Summary: The pull request that added this (facebook#17397) simply forgot to remove the callback, which would cause crashes if the RCTNetInfo module was ever deallocated. While that usually doesn't happen in apps, it can if the user logs out and you need to wipe all the RCT modules (to remove user data, for instance).

Libraries/Network/RCTNetInfo.m

@@ -164,6 +164,7 @@ - (BOOL)setReachabilityStatus:(SCNetworkReachabilityFlags)flags
                   reject:(__unused RCTPromiseRejectBlock)reject)
 {
   SCNetworkReachabilityRef reachability = [self getReachabilityRef];
+  SCNetworkReachabilityUnscheduleFromRunLoop(reachability, CFRunLoopGetMain(), kCFRunLoopCommonModes);
   CFRelease(reachability);
   resolve(@{@"connectionType": _connectionType ?: RCTConnectionTypeUnknown,
             @"effectiveConnectionType": _effectiveConnectionType ?: RCTEffectiveConnectionTypeUnknown,