cmd/dist: remove hardcoded timeout scale for arm and mips{,le,64,64le}

cmd/dist: remove hardcoded timeout scale for arm and mips{,le,64,64le}

Fixes #57117.

Change-Id: If36da5b138a5e92e27688719ffc1c4dafd590957
Reviewed-on: https://go-review.googlesource.com/c/go/+/455518
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>