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/rc/config.go

@@ -6,8 +6,8 @@ package rc
 
 import (
 	"context"
+	"fmt"
 
-	"github.com/pkg/errors"
 	"github.com/rclone/rclone/fs"
 	"github.com/rclone/rclone/fs/filter"
 )
@@ -146,16 +146,16 @@ func rcOptionsSet(ctx context.Context, in Params) (out Params, err error) {
 	for name, options := range in {
 		current := optionBlock[name]
 		if current == nil {
-			return nil, errors.Errorf("unknown option block %q", name)
+			return nil, fmt.Errorf("unknown option block %q", name)
 		}
 		err := Reshape(current, options)
 		if err != nil {
-			return nil, errors.Wrapf(err, "failed to write options from block %q", name)
+			return nil, fmt.Errorf("failed to write options from block %q: %w", name, err)
 		}
 		if reload := optionReload[name]; reload != nil {
 			err = reload(ctx)
 			if err != nil {
-				return nil, errors.Wrapf(err, "failed to reload options from block %q", name)
+				return nil, fmt.Errorf("failed to reload options from block %q: %w", name, err)
 			}
 		}
 	}