Remove github.com/pkg/errors and replace with std library version

This is possible now that we no longer support go1.12 and brings
rclone into line with standard practices in the Go world.

This also removes errors.New and errors.Errorf from lib/errors and
prefers the stdlib errors package over lib/errors.

fs/backend_config.go

@@ -6,11 +6,11 @@ package fs
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"strconv"
 	"strings"
 
-	"github.com/pkg/errors"
 	"github.com/rclone/rclone/fs/config/configmap"
 )
 
@@ -188,7 +188,7 @@ func ConfigConfirm(state string, Default bool, name string, help string) (*Confi
 // If there is only one item it will short cut to the next state
 func ConfigChooseFixed(state string, name string, help string, items []OptionExample) (*ConfigOut, error) {
 	if len(items) == 0 {
-		return nil, errors.Errorf("no items found in: %s", help)
+		return nil, fmt.Errorf("no items found in: %s", help)
 	}
 	choose := &ConfigOut{
 		State: state,
@@ -323,7 +323,7 @@ func configAll(ctx context.Context, name string, m configmap.Mapper, ri *RegInfo
 	if stateNumber != "" {
 		optionNumber, err = strconv.Atoi(stateNumber)
 		if err != nil {
-			return nil, errors.Wrap(err, "internal error: bad state number")
+			return nil, fmt.Errorf("internal error: bad state number: %w", err)
 		}
 	}
 
@@ -393,7 +393,7 @@ func configAll(ctx context.Context, name string, m configmap.Mapper, ri *RegInfo
 		}
 		return ConfigGoto("*postconfig")
 	}
-	return nil, errors.Errorf("internal error: bad state %q", state)
+	return nil, fmt.Errorf("internal error: bad state %q", state)
 }
 
 func backendConfigStep(ctx context.Context, name string, m configmap.Mapper, ri *RegInfo, choices configmap.Getter, in ConfigIn) (out *ConfigOut, err error) {
@@ -415,7 +415,7 @@ func backendConfigStep(ctx context.Context, name string, m configmap.Mapper, ri
 		in.State = ""
 		return backendConfigStep(ctx, name, m, ri, choices, in)
 	case strings.HasPrefix(in.State, "*"):
-		err = errors.Errorf("unknown internal state %q", in.State)
+		err = fmt.Errorf("unknown internal state %q", in.State)
 	default:
 		// Otherwise pass to backend
 		if ri.Config == nil {