opts: deprecate ValidateHost utility

The `ValidateHost` option was introduced in [moby@1ba1138] to be used
as validation func for the `--host` flag on the daemon in and CLI in
[moby@5e3f6e7], but is no longer used since [cli@6f61cf0]. which added
support for `ssh://` connections, and required validation elsewhere.

[moby@1ba1138]: moby/moby@1ba1138
[moby@5e3f6e7]: moby/moby@5e3f6e7
[cli@6f61cf0]: 6f61cf0

Signed-off-by: Sebastiaan van Stijn <[email protected]>

Author: thaJeztah

opts/hosts.go

@@ -34,7 +34,7 @@ const (
 
 // ValidateHost validates that the specified string is a valid host and returns it.
 //
-// TODO(thaJeztah): ValidateHost appears to be unused; deprecate it.
+// Deprecated: this function is no longer used, and will be removed in the next release.
 func ValidateHost(val string) (string, error) {
 	host := strings.TrimSpace(val)
 	// The empty string means default and is not handled by parseDockerDaemonHost