[iOS] Remove unused constants for first run view controller.

Use the accessibility label directly in the first run EarlGrey tests.
This makes it simpler to transition to the new sign-in architecture.
See go/chrome-ios-signin-migration for more details.

Bug: 1005509
Change-Id: I4afa65b02169927c919cb51dd9884bb828a55fd8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2144082
Reviewed-by: Jérôme Lebel <jlebel@chromium.org>
Commit-Queue: Nohemi Fernandez <fernandex@chromium.org>
Cr-Commit-Position: refs/heads/master@{#758767}

ios/chrome/browser/ui/first_run/first_run_chrome_signin_view_controller.mm

@@ -72,10 +72,6 @@ - (instancetype)initWithBrowser:(Browser*)browser
 - (void)viewDidLoad {
   [super viewDidLoad];
   [self.navigationController setNavigationBarHidden:YES];
-  self.primaryButton.accessibilityIdentifier =
-      first_run::kSignInButtonAccessibilityIdentifier;
-  self.secondaryButton.accessibilityIdentifier =
-      first_run::kSignInSkipButtonAccessibilityIdentifier;
 }
 
 - (void)viewDidAppear:(BOOL)animated {

ios/chrome/browser/ui/first_run/first_run_constants.h

@@ -9,10 +9,6 @@
 
 namespace first_run {
 
-// The accessibility identifier for the sign in button shown in first run.
-extern NSString* const kSignInButtonAccessibilityIdentifier;
-// The accessibility identifier for the skip sign in button shown in first run.
-extern NSString* const kSignInSkipButtonAccessibilityIdentifier;
 // The accessibility identifier for the UMA collection checkbox shown in first
 // run.
 extern NSString* const kUMAMetricsButtonAccessibilityIdentifier;

ios/chrome/browser/ui/first_run/first_run_constants.mm

@@ -10,10 +10,6 @@
 
 namespace first_run {
 
-NSString* const kSignInButtonAccessibilityIdentifier =
-    @"SignInButtonAccessibilityIdentifier";
-NSString* const kSignInSkipButtonAccessibilityIdentifier =
-    @"SkipButtonAccessibilityIdentifier";
 NSString* const kUMAMetricsButtonAccessibilityIdentifier =
     @"UMAMetricsButtonAccessibilityIdentifier";
 

ios/chrome/browser/ui/first_run/first_run_egtest.mm

@@ -32,8 +32,8 @@
 
 // Returns matcher for the skip sign in button.
 id<GREYMatcher> SkipSigninButton() {
-  return grey_accessibilityID(
-      first_run::kSignInSkipButtonAccessibilityIdentifier);
+  return ButtonWithAccessibilityLabel(
+      l10n_util::GetNSString(IDS_IOS_FIRSTRUN_ACCOUNT_CONSISTENCY_SKIP_BUTTON));
 }
 }