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/missing_network.h

@@ -49,35 +49,3 @@
 #ifndef IEEE80211_MAX_SSID_LEN
 #define IEEE80211_MAX_SSID_LEN 32
 #endif
-
-/* Not exposed but defined in include/net/netlabel.h */
-#ifndef NETLBL_NLTYPE_UNLABELED_NAME
-#define NETLBL_NLTYPE_UNLABELED_NAME "NLBL_UNLBL"
-#endif
-
-/* Not exposed but defined in net/netlabel/netlabel_unlabeled.h */
-enum {
-        NLBL_UNLABEL_C_UNSPEC,
-        NLBL_UNLABEL_C_ACCEPT,
-        NLBL_UNLABEL_C_LIST,
-        NLBL_UNLABEL_C_STATICADD,
-        NLBL_UNLABEL_C_STATICREMOVE,
-        NLBL_UNLABEL_C_STATICLIST,
-        NLBL_UNLABEL_C_STATICADDDEF,
-        NLBL_UNLABEL_C_STATICREMOVEDEF,
-        NLBL_UNLABEL_C_STATICLISTDEF,
-        __NLBL_UNLABEL_C_MAX,
-};
-
-/* Not exposed but defined in net/netlabel/netlabel_unlabeled.h */
-enum {
-        NLBL_UNLABEL_A_UNSPEC,
-        NLBL_UNLABEL_A_ACPTFLG,
-        NLBL_UNLABEL_A_IPV6ADDR,
-        NLBL_UNLABEL_A_IPV6MASK,
-        NLBL_UNLABEL_A_IPV4ADDR,
-        NLBL_UNLABEL_A_IPV4MASK,
-        NLBL_UNLABEL_A_IFACE,
-        NLBL_UNLABEL_A_SECCTX,
-        __NLBL_UNLABEL_A_MAX,
-};