[iOS] Fix React Native warnings

Fixes the following warning:

~~~
Module XXX requires main queue setup since it overrides `constantsToExport` but doesn't implement `requiresMainQueueSetup`. In a future release React Native will default to initializing all native modules on a background thread unless explicitly opted-out of.
~~~

For AppInfo and AuioMode, there is no need to initialize anything in the UI
thread, so just return NO.

ios/sdk/src/AppInfo.m

@@ -26,6 +26,10 @@
 
 RCT_EXPORT_MODULE();
 
++ (BOOL)requiresMainQueueSetup {
+    return NO;
+}
+
 - (NSDictionary *)constantsToExport {
     NSDictionary<NSString *, id> *infoDictionary
         = [[NSBundle mainBundle] infoDictionary];

ios/sdk/src/AudioMode.m

@@ -35,6 +35,10 @@ typedef enum {
     kAudioModeVideoCall
 } JitsiMeetAudioMode;
 
++ (BOOL)requiresMainQueueSetup {
+    return NO;
+}
+
 - (NSDictionary *)constantsToExport {
     return @{
         @"AUDIO_CALL" : [NSNumber numberWithInt: kAudioModeAudioCall],