Revert "login: normalize `registry-1.docker.io`"

This reverts commit e6624676e0.

Since e6624676e0, during login, we started
normalizing `registry-1.docker.io` to `index.docker.io`. This means that
if a user logs in with `docker login -u [username]
registry-1.docker.io`, the user's credentials get stored in
credhelpers/config.json under `https://index.docker.io/v1/`.

However, while the registry code normalizes an image reference without
registry (`docker pull alpine:latest`) and image references explicitly for
`index.docker.io` (`docker pull index.docker.io/library/alpine:latest`)
to the official index server (`https://index.docker.io/v1/`), and
fetches credentials for that auth key, it does not normalize
`registry-1.docker.io`, which means pulling explicitly from there
(`docker pull registry-1.docker.io/alpine:latest`) will not use
credentials stored under `https://index.docker.io/v1/`.

As such, until changes are made to the registry/pull/push code to
normalize `registry-1.docker.io` to `https://index.docker.io/v1/`, we
should not normalize this during login.

Signed-off-by: Laura Brehm <laurabrehm@hey.com>

cli/command/registry/login.go

@@ -90,9 +90,7 @@ func runLogin(ctx context.Context, dockerCli command.Cli, opts loginOptions) err
 		serverAddress string
 		response      *registrytypes.AuthenticateOKBody
 	)
-	if opts.serverAddress != "" &&
-		opts.serverAddress != registry.DefaultNamespace &&
-		opts.serverAddress != registry.DefaultRegistryHost {
+	if opts.serverAddress != "" && opts.serverAddress != registry.DefaultNamespace {
 		serverAddress = opts.serverAddress
 	} else {
 		serverAddress = registry.IndexServer