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/bisync/bisync_test.go

@@ -7,6 +7,7 @@ package bisync_test
 import (
 	"bytes"
 	"context"
+	"errors"
 	"flag"
 	"fmt"
 	"io/ioutil"
@@ -36,7 +37,6 @@ import (
 	"github.com/rclone/rclone/lib/atexit"
 	"github.com/rclone/rclone/lib/random"
 
-	"github.com/pkg/errors"
 	"github.com/pmezard/go-difflib/difflib"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -541,7 +541,7 @@ func (b *bisyncTest) runTestStep(ctx context.Context, line string) (err error) {
 	case "bisync":
 		return b.runBisync(ctx, args[1:])
 	default:
-		return errors.Errorf("unknown command: %q", args[0])
+		return fmt.Errorf("unknown command: %q", args[0])
 	}
 }
 
@@ -635,7 +635,7 @@ func (b *bisyncTest) runBisync(ctx context.Context, args []string) (err error) {
 			fs1 = addSubdir(b.path1, val)
 			fs2 = addSubdir(b.path2, val)
 		default:
-			return errors.Errorf("invalid bisync option %q", arg)
+			return fmt.Errorf("invalid bisync option %q", arg)
 		}
 	}
 
@@ -793,12 +793,12 @@ func touchFiles(ctx context.Context, dateStr string, f fs.Fs, dir, glob string)
 
 	date, err := time.ParseInLocation(touchDateFormat, dateStr, bisync.TZ)
 	if err != nil {
-		return files, errors.Wrapf(err, "invalid date %q", dateStr)
+		return files, fmt.Errorf("invalid date %q: %w", dateStr, err)
 	}
 
 	matcher, firstErr := filter.GlobToRegexp(glob, false)
 	if firstErr != nil {
-		return files, errors.Errorf("invalid glob %q", glob)
+		return files, fmt.Errorf("invalid glob %q", glob)
 	}
 
 	entries, firstErr := f.List(ctx, "")