Revert "networkd: NetLabel integration"

This reverts PR #23269 and its follow-up commit. Especially,
2299b1cae3 (partially), and
3cf63830ac.

The PR was merged without final approval, and has several issues:
- The NetLabel for static addresses are not assigned, as labels are
  stored in the Address objects managed by Network, instead of Link.
- If NetLabel is specified for a static address, then the address
  section will be invalid and the address will not be configured,
- It should be implemented with Request object,
- There is no test about the feature.

src/basic/in-addr-util.c

@@ -585,45 +585,6 @@ struct in_addr* in4_addr_prefixlen_to_netmask(struct in_addr *addr, unsigned cha
         return addr;
 }
 
-struct in6_addr* in6_addr_prefixlen_to_netmask(struct in6_addr *addr, unsigned char prefixlen) {
-        assert(addr);
-        assert(prefixlen <= 128);
-
-        for (unsigned int i = 0; i < 16; i++) {
-                uint8_t mask;
-
-                if (prefixlen >= 8) {
-                        mask = 0xFF;
-                        prefixlen -= 8;
-                } else if (prefixlen > 0) {
-                        mask = 0xFF << (8 - prefixlen);
-                        prefixlen = 0;
-                } else {
-                        assert(prefixlen == 0);
-                        mask = 0;
-                }
-
-                addr->s6_addr[i] = mask;
-        }
-
-        return addr;
-}
-
-int in_addr_prefixlen_to_netmask(int family, union in_addr_union *addr, unsigned char prefixlen) {
-        assert(addr);
-
-        switch (family) {
-        case AF_INET:
-                in4_addr_prefixlen_to_netmask(&addr->in, prefixlen);
-                return 0;
-        case AF_INET6:
-                in6_addr_prefixlen_to_netmask(&addr->in6, prefixlen);
-                return 0;
-        default:
-                return -EAFNOSUPPORT;
-        }
-}
-
 int in4_addr_default_prefixlen(const struct in_addr *addr, unsigned char *prefixlen) {
         uint8_t msb_octet = *(uint8_t*) addr;