Demote i686-unknown-freebsd to tier 2 compiler target
While technically the `i686-unknown-freebsd` target has been a tier 2 development platform for a long time, with full toolchain tarballs available on static.rust-lang.org, due to a bug in the manifest generation the target was never available for download through rustup.
The infrastructure team privately inquired the FreeBSD package maintainers, and they weren't relying on those tarballs either, so it's a fair assumption to say practically nobody is using those tarballs.
This PR then removes the CI builder that produces full tarballs for the target, and moves the compilation of `rust-std` for the target in `dist-various-2`. The `x86_64-unknown-freebsd` target is *not* affected.
cc `@rust-lang/infra` `@rust-lang/compiler` `@rust-lang/release`
r? `@Mark-Simulacrum`
4e0695b79f