[iOS] Remove DCHECK that overtriggers on account adds

Remove DCHECK in -[AddAccountSigninCoordinator start].
It overtriggers when the user wants to sign-in back with the primary
account after being removed from the phone by another app.

This DCHECK has been introduced with: crrev.com/c/2464274

Fixed: 1147837
Change-Id: I4d2199e66ad2e7a825e26e973dc4b1ddd2e518ce
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2536446
Commit-Queue: Jérôme Lebel <jlebel@chromium.org>
Reviewed-by: Nohemi Fernandez <fernandex@chromium.org>
Auto-Submit: Jérôme Lebel <jlebel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#827792}

ios/chrome/browser/ui/authentication/signin/add_account_signin/add_account_signin_coordinator.mm

@@ -101,16 +101,6 @@ using signin_metrics::PromoAction;
 
 - (void)start {
   [super start];
-  AuthenticationService* authenticationService =
-      AuthenticationServiceFactory::GetForBrowserState(
-          self.browser->GetBrowserState());
-  // For AddAccountSigninIntentAddSecondaryAccount, the coordinator can be used
-  // to add a secondary account in the settings while being signed in, or
-  // from the user consent view while being not signed in.
-  // For AddAccountSigninIntentReauthPrimaryAccount, the coordinator can only
-  // be used when the user is signed in.
-  DCHECK(authenticationService->IsAuthenticated() ||
-         self.signinIntent == AddAccountSigninIntentAddSecondaryAccount);
   self.identityInteractionManager =
       ios::GetChromeBrowserProvider()
           ->GetChromeIdentityService()