Remove unused 'Credential::create' methods.

Source/modules/credentialmanager/Credential.h

Index: Source/modules/credentialmanager/Credential.h
diff --git a/Source/modules/credentialmanager/Credential.h b/Source/modules/credentialmanager/Credential.h
index 95abfb6e944057e69df6c1be92427e282b581c38..54c24198bb53690dfbae8426ae8a7a42141ee4a0 100644
--- a/Source/modules/credentialmanager/Credential.h
+++ b/Source/modules/credentialmanager/Credential.h
@@ -17,9 +17,6 @@ class ExceptionState;
 class Credential : public GarbageCollected<Credential>, public ScriptWrappable {
     DEFINE_WRAPPERTYPEINFO();
 public:
-    static Credential* create(const String& id, const String& name, const KURL& icon);
-    static Credential* create(const String& id, const String& name, const String& icon, ExceptionState&);
-
     // Credential.idl
     const String& id() const { return m_platformCredential->id(); }
     const String& name() const { return m_platformCredential->name(); }