fdisk: disconnect from the build

[emaste]

Summary

It is an obsolete tool for managing a legacy disk partitioning scheme.
gpart should be used instead, regardless of whether a legacy or
contemporary scheme is in use.

[rgrimes]

Please put a a gonein(15) into the fdisk binary with a way for "users" to inform the project of there use before we just remove this silently.

[emaste]

In D43575#993903, @rgrimes wrote:

Please put a a gonein(15) into the fdisk binary with a way for "users" to inform the project of there use before we just remove this silently.

gone_in is only in kernel, but warning message proposed in review D43585

[imp]

I think this might break nanobsd.
I'm traveling this week, so it may be next before i get it fixed.

[emaste]

I won't commit this before all dependencies are addressed - mainly I want to get deprecation notices into the tree and MFC'd.