remove drone-hugo validate arg

The dependence of drone-hugo validate, hugo check, was removed since v0.92.0.
  As the hugo check does nothing in fact, a removal of command validate
  could be considered.

  - removed command validate in main.go and plugin_test.go
  - removed unused github.com/pkg/errors in plugin_test.go

main.go

@@ -81,11 +81,6 @@ func main() {
 			EnvVar: "PLUGIN_URL",
 			Value:  "",
 		},
-		cli.BoolFlag{
-			Name:   "validate",
-			Usage:  "validate config file before generation",
-			EnvVar: "PLUGIN_VALIDATE",
-		},
 		cli.StringFlag{
 			Name:   "hugoversion",
 			Usage:  "the hugo version to be used",
@@ -110,7 +105,6 @@ func run(c *cli.Context) error {
 			Drafts:   c.Bool("drafts"),
 			Expired:  c.Bool("expired"),
 			Future:   c.Bool("future"),
-			Validate: c.Bool("validate"),
 			Config:   c.String("config"),
 			Content:  c.String("content"),
 			Layout:   c.String("layout"),

plugin_test.go

@@ -2,28 +2,8 @@ package main
 
 import (
 	"testing"
-
-	"github.com/pkg/errors"
 )
 
-func TestCommandValidate(t *testing.T) {
-	config := Config{Validate: true}
-	want := []string{"hugo", "check"}
-	got := commandValidate(config)
-
-	if err := argsEqual(want, got.Args); err != nil {
-		t.Errorf("%s", err)
-	}
-
-	config = Config{Validate: true, Config: "config.toml"}
-	want = []string{"hugo", "check", "--config", "config.toml"}
-	got = commandValidate(config)
-
-	if err := argsEqual(want, got.Args); err != nil {
-		t.Errorf("%s", err)
-	}
-}
-
 func TestVersionEqual(t *testing.T) {
 	want := true
 	if got := versionsEqual("1.0", "1.0"); want != got {
@@ -35,12 +15,3 @@ func TestVersionEqual(t *testing.T) {
 		t.Errorf("want: %t, got: %t", want, got)
 	}
 }
-
-func argsEqual(want []string, got []string) error {
-	for i := range want {
-		if want[i] != got[i] {
-			return errors.Errorf("Arguments do not match, want: %s, got: %s", want[i], got[i])
-		}
-	}
-	return nil
-}