Don't save library version to NSUserDefaults (#212)

This seems to be a holdover from some old code, and it's not being used anywhere in the component. Plus it's better not to be saving anything in `[NSUserDefaults standardUserDefaults]` as that is the developer/app's domain.

Also renamed the messaging code while I was in there to be something meaningful ("000" → "PrintLibraryVersion").

Author: rsattar

Firebase/Messaging/FIRMMessageCode.h

@@ -21,7 +21,7 @@ typedef NS_ENUM(NSInteger, FIRMessagingMessageCode) {
   kFIRMessagingMessageCodeFIRApp000 = 1000,  // I-FCM001000
   kFIRMessagingMessageCodeFIRApp001 = 1001,  // I-FCM001001
   // FIRMessaging.m
-  kFIRMessagingMessageCodeMessaging000 = 2000,  // I-FCM002000
+  kFIRMessagingMessageCodeMessagingPrintLibraryVersion = 2000,  // I-FCM002000
   kFIRMessagingMessageCodeMessaging001 = 2001,  // I-FCM002001
   kFIRMessagingMessageCodeMessaging002 = 2002,  // I-FCM002002 - no longer used
   kFIRMessagingMessageCodeMessaging003 = 2003,  // I-FCM002003

Firebase/Messaging/FIRMessaging.m

@@ -187,8 +187,12 @@ - (void)setRemoteMessageDelegate:(id<FIRMessagingDelegate>)delegate {
 #pragma mark - Config
 
 - (void)start {
+  // Print the library version for logging.
+  NSString *currentLibraryVersion = FIRMessagingCurrentLibraryVersion();
+  FIRMessagingLoggerInfo(kFIRMessagingMessageCodeMessagingPrintLibraryVersion,
+                         @"FIRMessaging library version %@",
+                         currentLibraryVersion);
 
-  [self saveLibraryVersion];
   [self setupReceiver];
 
   NSString *hostname = kFIRMessagingReachabilityHostname;
@@ -244,14 +248,6 @@ - (void)setupNotificationListeners {
                object:nil];
 }
 
-- (void)saveLibraryVersion {
-  NSString *currentLibraryVersion = FIRMessagingCurrentLibraryVersion();
-  [[NSUserDefaults standardUserDefaults] setObject:currentLibraryVersion
-                                            forKey:kFIRMessagingLibraryVersion];
-  FIRMessagingLoggerInfo(kFIRMessagingMessageCodeMessaging000, @"FIRMessaging library version %@",
-                         currentLibraryVersion);
-}
-
 - (void)setupReceiver {
   self.receiver = [[FIRMessagingReceiver alloc] init];
   self.receiver.delegate = self;

Firebase/Messaging/FIRMessagingConstants.h

@@ -42,8 +42,6 @@ FOUNDATION_EXPORT NSString *const kFIRMessagingMessageSyncViaMCSKey;
 FOUNDATION_EXPORT NSString *const kFIRMessagingMessageSyncMessageTTLKey;
 FOUNDATION_EXPORT NSString *const kFIRMessagingMessageLinkKey;
 
-FOUNDATION_EXPORT NSString *const kFIRMessagingLibraryVersion;
-
 FOUNDATION_EXPORT NSString *const kFIRMessagingRemoteNotificationsProxyEnabledInfoPlistKey;
 
 FOUNDATION_EXPORT NSString *const kFIRMessagingApplicationSupportSubDirectory;

Firebase/Messaging/FIRMessagingConstants.m

@@ -35,8 +35,6 @@
 NSString *const kFIRMessagingMessageSyncMessageTTLKey = @"gcm." @"ttl";
 NSString *const kFIRMessagingMessageLinkKey = @"gcm." @"app_link";
 
-NSString *const kFIRMessagingLibraryVersion = @"FIRMessaging-version";
-
 NSString *const kFIRMessagingRemoteNotificationsProxyEnabledInfoPlistKey =
     @"FirebaseAppDelegateProxyEnabled";