networkd-ndisc: drop confused freepp function

The function to cleanup IPv6Token was defined using freep, i.e. the macro
generated a freepp function. The correct way would be to do something like
  #define ipv6_token_free mfree
  DEFINE_TRIVIAL_CLEANUP_FUNC(IPv6Token *, ipv6_token_free);
which would create ipv6_token_freep().
But since the cleanup function is unused, let's just drop it.

src/network/networkd-ndisc.h

@@ -63,7 +63,6 @@ struct IPv6Token {
 };
 
 int ipv6token_new(IPv6Token **ret);
-DEFINE_TRIVIAL_CLEANUP_FUNC(IPv6Token *, freep);
 
 static inline char* NDISC_DNSSL_DOMAIN(const NDiscDNSSL *n) {
         return ((char*) n) + ALIGN(sizeof(NDiscDNSSL));