rm -rf mipsn32

[Kyle Evans]

Hi,

I've been doing some work lately to try to get mips switched over to
full LLVM world/kernel... LLVM 9.0 is looking pretty good with some
patches and I have a couple in review that I need to get back to. With
my current mips-llvm branch and llvm9:

- MALTA is happy, full llvm9 world+kernel
- MALTA64 is mostly happy, but requires a carefully placed printf in
bit_ffc_at to get past selecting pids in early-ish boot.

These are easier-ish problems to solve... n32 is a complete crapshoot.
I have one patch pending to fix one LLVM-inflicted issue, but it's got
deeper problems as you progress trying to build an n32 world and it's
getting kind of bizarre. So, questions...

- How much use does n32 even see in FreeBSD-land?
- Can we just kind of drop it?

Thanks,

Kyle Evans