[Autofill] Improve support for various credit card expiration dates.

components/autofill/core/browser/validation.h

Index: components/autofill/core/browser/validation.h
diff --git a/components/autofill/core/browser/validation.h b/components/autofill/core/browser/validation.h
index e9388fda2d6724b3be3b1fa714a1a7630913d02a..aaaedcd23b82c8442bec515954d3cf06b43f6797 100644
--- a/components/autofill/core/browser/validation.h
+++ b/components/autofill/core/browser/validation.h
@@ -15,9 +15,6 @@ namespace autofill {
 
 // Returns true if |year| and |month| describe a date later than |now|.
 // |year| must have 4 digits.
-bool IsValidCreditCardExpirationDate(const base::string16& year,
-                                     const base::string16& month,
-                                     const base::Time& now);
 bool IsValidCreditCardExpirationDate(int year,
                                      int month,
                                      const base::Time& now);