cli/command/plugin: remove special error handling on install, upgrade

Similar to 323fbc4 - this code was added
in [moby@c127d96], but used string-matching to detect cases where a user
tried to install an image as plugin. However, this handling no longer matched
any error-strings, so no longer worked:

    docker plugin install busybox
    Error response from daemon: did not find plugin config for specified reference docker.io/library/busybox:latest

[moby@c127d96]: moby/moby@c127d96

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

Author: thaJeztah

cli/command/plugin/install.go

@@ -3,7 +3,6 @@ package plugin
 import (
 	"context"
 	"fmt"
-	"strings"
 
 	"github.com/distribution/reference"
 	"github.com/docker/cli/cli"
@@ -94,9 +93,6 @@ func runInstall(ctx context.Context, dockerCLI command.Cli, opts pluginOptions)
 	}
 	responseBody, err := dockerCLI.Client().PluginInstall(ctx, localName, options)
 	if err != nil {
-		if strings.Contains(err.Error(), "(image) when fetching") {
-			return errors.New(err.Error() + " - Use \"docker image pull\"")
-		}
 		return err
 	}
 	defer func() {

cli/command/plugin/upgrade.go

@@ -3,7 +3,6 @@ package plugin
 import (
 	"context"
 	"fmt"
-	"strings"
 
 	"github.com/distribution/reference"
 	"github.com/docker/cli/cli"
@@ -83,9 +82,6 @@ func runUpgrade(ctx context.Context, dockerCLI command.Cli, opts pluginOptions)
 
 	responseBody, err := dockerCLI.Client().PluginUpgrade(ctx, opts.localName, options)
 	if err != nil {
-		if strings.Contains(err.Error(), "target is image") {
-			return errors.New(err.Error() + " - Use `docker image pull`")
-		}
 		return err
 	}
 	defer func() {