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/sizesuffix.go

@@ -3,13 +3,12 @@ package fs
 // SizeSuffix is parsed by flag with K/M/G binary suffixes
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"math"
 	"sort"
 	"strconv"
 	"strings"
-
-	"github.com/pkg/errors"
 )
 
 // SizeSuffix is an int64 with a friendly way of printing setting
@@ -153,7 +152,7 @@ func (x *SizeSuffix) Set(s string) error {
 			suffix = s[len(s)-3]
 			suffixLen = 3
 			if multiplierFound, multiplier = x.multiplierFromSymbol(suffix); !multiplierFound {
-				return errors.Errorf("bad suffix %q", suffix)
+				return fmt.Errorf("bad suffix %q", suffix)
 			}
 			// Could also support SI form MB, and treat it equivalent to MiB, but perhaps better to reserve it for CountSuffix?
 			//} else if len(s) > 1 {
@@ -172,11 +171,11 @@ func (x *SizeSuffix) Set(s string) error {
 			multiplierFound, multiplier = x.multiplierFromSymbol(suffix)
 		}
 		if !multiplierFound {
-			return errors.Errorf("bad suffix %q", suffix)
+			return fmt.Errorf("bad suffix %q", suffix)
 		}
 	default:
 		if multiplierFound, multiplier = x.multiplierFromSymbol(suffix); !multiplierFound {
-			return errors.Errorf("bad suffix %q", suffix)
+			return fmt.Errorf("bad suffix %q", suffix)
 		}
 	}
 	s = s[:len(s)-suffixLen]
@@ -185,7 +184,7 @@ func (x *SizeSuffix) Set(s string) error {
 		return err
 	}
 	if value < 0 {
-		return errors.Errorf("size can't be negative %q", s)
+		return fmt.Errorf("size can't be negative %q", s)
 	}
 	value *= multiplier
 	*x = SizeSuffix(value)