remove amd64 hardcodes

[rminnich]

For reasons, there is amd64 hardcoding everywhere and it has to die.

docker/Dockerfile:COPY linux_amd64 /linux_amd64
docker/Makefile:    echo on start, run /linux_amd64/bin/init
docker/Makefile:    sudo rm -rf dev docker etc go key key.pub linux_amd64 pkg src tmp
init/root_linux.go:        dir{Name: "/go/pkg/linux_amd64", Mode: 0o777},
init/init_linux.go:            Command("/linux_amd64/bin/elvish"),
init/init_linux.go:            Command("/linux_amd64/bin/date"),
installcommand/cpu:#!/linux_amd64/bin/installcommand #!/src/[github.com/u-root/cpu/cmds/cpud](http://github.com/u-root/cpu/cmds/cpud)
installcommand/date:#!/linux_amd64/bin/installcommand #!/src/[github.com/u-root/u-root/cmds/core/date](http://github.com/u-root/u-root/cmds/core/date)
installcommand/installcommand.go:// ["/linux_amd64/bin/installcommand" "#!/src/[github.com/u-root/u-root/cmds/core/date](http://github.com/u-root/u-root/cmds/core/date)" "/linux_amd64/bin/date"]
README.md:unshare -m chroot "/tmp/sourcery3965857644" /linux_amd64/bin/init.
oops -- that was incomplete:
erivan01@thundercleese:~/src/sourcery$ git branch
* arm64
  main
erivan01@thundercleese:~/src/sourcery$ grep -ir arm64 *
erivan01@thundercleese:~/src/sourcery$ grep -ir amd64 *
docker/Dockerfile:COPY linux_amd64 /linux_amd64
docker/Makefile:    echo on start, run /linux_amd64/bin/init
docker/Makefile:    sudo rm -rf dev docker etc go key key.pub linux_amd64 pkg src tmp
init/root_linux.go:        dir{Name: "/go/pkg/linux_amd64", Mode: 0o777},
init/init_linux.go:            Command("/linux_amd64/bin/elvish"),
init/init_linux.go:            Command("/linux_amd64/bin/date"),
installcommand/cpu:#!/linux_amd64/bin/installcommand #!/src/[github.com/u-root/cpu/cmds/cpud](http://github.com/u-root/cpu/cmds/cpud)
installcommand/date:#!/linux_amd64/bin/installcommand #!/src/[github.com/u-root/u-root/cmds/core/date](http://github.com/u-root/u-root/cmds/core/date)
installcommand/installcommand.go:// ["/linux_amd64/bin/installcommand" "#!/src/[github.com/u-root/u-root/cmds/core/date](http://github.com/u-root/u-root/cmds/core/date)" "/linux_amd64/bin/date"]
README.md:unshare -m chroot "/tmp/sourcery3965857644" /linux_amd64/bin/init.