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.

cmd/about/about.go

@@ -3,10 +3,10 @@ package about
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"os"
 
-	"github.com/pkg/errors"
 	"github.com/rclone/rclone/cmd"
 	"github.com/rclone/rclone/fs"
 	"github.com/rclone/rclone/fs/config/flags"
@@ -98,11 +98,11 @@ see complete list in [documentation](https://rclone.org/overview/#optional-featu
 		cmd.Run(false, false, command, func() error {
 			doAbout := f.Features().About
 			if doAbout == nil {
-				return errors.Errorf("%v doesn't support about", f)
+				return fmt.Errorf("%v doesn't support about", f)
 			}
 			u, err := doAbout(context.Background())
 			if err != nil {
-				return errors.Wrap(err, "About call failed")
+				return fmt.Errorf("About call failed: %w", err)
 			}
 			if u == nil {
 				return errors.New("nil usage returned")