Remove sys/mips/rmi. It's been unmaintained since 2011. This hardware
is now unobtanium. It's only had API changes in the last 7 years, and
is responsible for a very large number of them. In addition, there's a
lot of code that reimplements base FreeBSD functionality, diminishing
the chances it still works. Without hardware to teset it on, or
prospects of obtaining such hardware and without vendor support, it's
time to move on.
Suggested by: kan@ in mips@ retirement discussion