Mk/bsd.default-versions.mk: switch riscv64 to librsvg2-rust after 6718da31bafa + 54442654f6d6

Sync with ONLY_FOR_ARCHS in lang/rust. The default is optimized for runtime.
qemu-riscv64-static is broken on FreeBSD >= 13.1, so the package cluster
is irrelevant since 2022-09-03.