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.

lib/oauthutil/oauthutil.go

@@ -3,6 +3,7 @@ package oauthutil
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"html/template"
 	"net"
@@ -12,7 +13,6 @@ import (
 	"sync"
 	"time"
 
-	"github.com/pkg/errors"
 	"github.com/rclone/rclone/fs"
 	"github.com/rclone/rclone/fs/config"
 	"github.com/rclone/rclone/fs/config/configmap"
@@ -110,7 +110,7 @@ type oldToken struct {
 func GetToken(name string, m configmap.Mapper) (*oauth2.Token, error) {
 	tokenString, ok := m.Get(config.ConfigToken)
 	if !ok || tokenString == "" {
-		return nil, errors.Errorf("empty token found - please run \"rclone config reconnect %s:\"", name)
+		return nil, fmt.Errorf("empty token found - please run \"rclone config reconnect %s:\"", name)
 	}
 	token := new(oauth2.Token)
 	err := json.Unmarshal([]byte(tokenString), token)
@@ -245,7 +245,7 @@ func (ts *TokenSource) Token() (*oauth2.Token, error) {
 		time.Sleep(1 * time.Second)
 	}
 	if err != nil {
-		return nil, errors.Wrapf(err, "couldn't fetch token - maybe it has expired? - refresh with \"rclone config reconnect %s:\"", ts.name)
+		return nil, fmt.Errorf("couldn't fetch token - maybe it has expired? - refresh with \"rclone config reconnect %s:\": %w", ts.name, err)
 	}
 	changed = changed || (*token != *ts.token)
 	ts.token = token
@@ -256,7 +256,7 @@ func (ts *TokenSource) Token() (*oauth2.Token, error) {
 		}
 		err = PutToken(ts.name, ts.m, token, false)
 		if err != nil {
-			return nil, errors.Wrap(err, "couldn't store token")
+			return nil, fmt.Errorf("couldn't store token: %w", err)
 		}
 	}
 	return token, nil
@@ -442,7 +442,7 @@ func ConfigOAuth(ctx context.Context, name string, m configmap.Mapper, ri *fs.Re
 		}
 		opt, ok := out.OAuth.(*Options)
 		if !ok {
-			return nil, errors.Errorf("internal error: oauth failed: wrong type in config: %T", out.OAuth)
+			return nil, fmt.Errorf("internal error: oauth failed: wrong type in config: %T", out.OAuth)
 		}
 		if opt.OAuth2Config == nil {
 			return nil, errors.New("internal error: oauth failed: OAuth2Config not set")
@@ -499,7 +499,7 @@ version recommended):
 		// Encode them into a string
 		mCopyString, err := inM.Encode()
 		if err != nil {
-			return nil, errors.Wrap(err, "oauthutil authorize encode")
+			return nil, fmt.Errorf("oauthutil authorize encode: %w", err)
 		}
 		// Write what the user has to do
 		if len(mCopyString) > 0 {
@@ -547,7 +547,7 @@ version recommended):
 			oauthConfig = fixRedirect(oauthConfig)
 			code, err = configSetup(ctx, ri.Name, name, m, oauthConfig, opt)
 			if err != nil {
-				return nil, errors.Wrap(err, "config failed to refresh token")
+				return nil, fmt.Errorf("config failed to refresh token: %w", err)
 			}
 		}
 		err = configExchange(ctx, name, m, oauthConfig, code)
@@ -560,7 +560,7 @@ version recommended):
 		_, returnState := fs.StatePop(stateParams)
 		return fs.ConfigGoto(returnState)
 	}
-	return nil, errors.Errorf("unknown internal oauth state %q", state)
+	return nil, fmt.Errorf("unknown internal oauth state %q", state)
 }
 
 func init() {
@@ -626,7 +626,7 @@ func configSetup(ctx context.Context, id, name string, m configmap.Mapper, oauth
 	server := newAuthServer(opt, bindAddress, state, authURL)
 	err = server.Init()
 	if err != nil {
-		return "", errors.Wrap(err, "failed to start auth webserver")
+		return "", fmt.Errorf("failed to start auth webserver: %w", err)
 	}
 	go server.Serve()
 	defer server.Stop()
@@ -662,7 +662,7 @@ func configExchange(ctx context.Context, name string, m configmap.Mapper, oauthC
 	ctx = Context(ctx, fshttp.NewClient(ctx))
 	token, err := oauthConfig.Exchange(ctx, code)
 	if err != nil {
-		return errors.Wrap(err, "failed to get token")
+		return fmt.Errorf("failed to get token: %w", err)
 	}
 	return PutToken(name, m, token, true)
 }