tlsconfig: remove support for tls.VersionSSL30

[alrs]

The Go authors deprecated support for SSLv3 in go 1.13. They've decided to remove it in go 1.14, and have already merged the commit.

See: https://golang.org/issue/32716

This PR, or something like it, should probably land before February 2020.

[AkihiroSuda]

CI failure seems unrelated?

#!/bin/bash -eo pipefail
go get -d github.com/Microsoft/go-winio &&
go build ./...
# golang.org/x/sys/windows
/home/circleci/.go_workspace/src/golang.org/x/sys/windows/dll_windows.go:21:6: missing function body for "syscall_loadlibrary"
/home/circleci/.go_workspace/src/golang.org/x/sys/windows/dll_windows.go:24:6: missing function body for "syscall_getprocaddress"
Exited with code 2

[AkihiroSuda]

commit needs sign

[alrs]

@AkihiroSuda I see my commit as signed, is your comment addressed to me?

[AkihiroSuda]

@alrs Please sign the commit with git commit -s https://github.com/moby/moby/blob/master/docs/contributing/set-up-git.md#task-2-set-your-signature-and-an-upstream-remote