[ios] Do iosapp token handling in viewDidLoad

Doing this work in viewDidAppear meant that it happened every time the
modal debug settings view disappeared (and the map view reappeared).

platform/ios/app/MBXViewController.m

@@ -140,12 +140,7 @@ - (void)viewDidLoad
     [self restoreState:nil];
 
     self.debugLoggingEnabled = [[NSUserDefaults standardUserDefaults] boolForKey:@"MGLMapboxMetricsDebugLoggingEnabled"];
-}
 
-- (void)viewDidAppear:(BOOL)animated
-{
-    [super viewDidAppear:animated];
-
     if ([MGLAccountManager accessToken].length)
     {
         self.styleIndex = -1;