Deprecate/remove fmtree(8)?

[Kyle Evans]

Hi,

I was reviewing build options, and noticed that we're still building
and installing fmtree by default.

Brooks imported nmtree about 8 years ago, made it the default about 7
years ago. Since then, fmtree has seen approximately ~0 work besides
build fixes from tangentially related work or fixes for bugs that
nmtree inherited from fmtree.

Is anyone actually using this? This feels like a pretty clear case of
maintenance burden at a glance...

Thanks,

Kyle Evans