cmd/dist: drop support for pre-compiled test binaries
We haven't used this in a while and it's going to complicate later
changes to dist, so drop support. This was primarily for supporting
slow QEMU-based builders, but an alternative and simpler way to do
that if we need to in the future is to supply a go_exec wrapper to run
tests in QEMU, like we do for other emulated platforms.
Simplification for #37486.
Change-Id: Idc0383f59c61d8546ea3b4d2eede4acdaf30d9b6
Reviewed-on: https://go-review.googlesource.com/c/go/+/431256
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Austin Clements <austin@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Run-TryBot: Austin Clements <austin@google.com>