LibJS: Make Date.getUTCSeconds() call through to LibC

The tzset documentation says that TZ allows a per-second local timezone,
so don't be needlessly clever here.

No observable behavior difference at this point, but if we ever
implement tzset, this will have a small effect.

Libraries/LibJS/Runtime/Date.cpp

@@ -87,6 +87,11 @@ int Date::utc_month() const
     return to_utc_tm().tm_mon;
 }
 
+int Date::utc_seconds() const
+{
+    return to_utc_tm().tm_sec;
+}
+
 String Date::iso_date_string() const
 {
     auto tm = to_utc_tm();