change use of errors.Wrap to fmt.Errorf with %w verb

Closes #4603

Commands used (VIM):

```
:args `rg -l errors.Wrap`
:argdo normal @q | update
```

where q is a macros rewriting the `errors.Wrap` to `fmt.Errorf`.

libs/async/async.go

@@ -1,9 +1,8 @@
 package async
 
 import (
+	"fmt"
 	"sync/atomic"
-
-	"github.com/pkg/errors"
 )
 
 //----------------------------------------
@@ -144,7 +143,7 @@ func Parallel(tasks ...Task) (trs *TaskResultSet, ok bool) {
 				if pnk := recover(); pnk != nil {
 					atomic.AddInt32(numPanics, 1)
 					// Send panic to taskResultCh.
-					taskResultCh <- TaskResult{nil, errors.Errorf("panic in task %v", pnk)}
+					taskResultCh <- TaskResult{nil, fmt.Errorf("panic in task %v", pnk)}
 					// Closing taskResultCh lets trs.Wait() work.
 					close(taskResultCh)
 					// Decrement waitgroup.

libs/async/async_test.go

@@ -1,12 +1,12 @@
 package async
 
 import (
+	"errors"
 	"fmt"
 	"sync/atomic"
 	"testing"
 	"time"
 
-	"github.com/pkg/errors"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -125,7 +125,7 @@ func TestParallelRecover(t *testing.T) {
 	// Verify task #0, #1, #2.
 	checkResult(t, taskResultSet, 0, 0, nil, nil)
 	checkResult(t, taskResultSet, 1, 1, errors.New("some error"), nil)
-	checkResult(t, taskResultSet, 2, nil, nil, errors.Errorf("panic in task %v", 2).Error())
+	checkResult(t, taskResultSet, 2, nil, nil, fmt.Errorf("panic in task %v", 2).Error())
 }
 
 // Wait for result