Remove old getter/setter for SigninErrorProvider.

ios/public/provider/chrome/browser/signin/signin_error_provider.mm

Index: ios/public/provider/chrome/browser/signin/signin_error_provider.mm
diff --git a/ios/public/provider/chrome/browser/signin/signin_error_provider.mm b/ios/public/provider/chrome/browser/signin/signin_error_provider.mm
index 4677105cd51ea9756f8da3e9f7f70b17a5de593c..f9eeba60a5f0b1ab53a04be64f5efaa104f3243f 100644
--- a/ios/public/provider/chrome/browser/signin/signin_error_provider.mm
+++ b/ios/public/provider/chrome/browser/signin/signin_error_provider.mm
@@ -6,18 +6,6 @@
 
 namespace ios {
 
-namespace {
-SigninErrorProvider* g_signin_error_provider = nullptr;
-}
-
-void SetSigninErrorProvider(SigninErrorProvider* provider) {
-  g_signin_error_provider = provider;
-}
-
-SigninErrorProvider* GetSigninErrorProvider() {
-  return g_signin_error_provider;
-}
-
 SigninErrorProvider::SigninErrorProvider() {}
 
 SigninErrorProvider::~SigninErrorProvider() {}