Revert "networkd: NetLabel integration"

Revert "networkd: NetLabel integration"

This reverts PR #23269 and its follow-up commit. Especially,
2299b1cae32c1fb8911da0ce26efced68032f4f8 (partially), and
3cf63830acdef9d8afdc9ef1cf25aa7e85a5e4d5.

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.