Remove the unnecessary Errorf in Frame.document

Resolves https://github.com/grafana/xk6-browser/pull/149/files#r765672948

common/frame.go

@@ -319,7 +319,7 @@ func (f *Frame) document() (*ElementHandle, error) {
 		return nil, fmt.Errorf("frame document: cannot evaluate in main execution context: %w", err)
 	}
 	if result == nil {
-		return nil, fmt.Errorf("frame document: evaluate result is nil in main execution context: %w", err)
+		return nil, errors.New("frame document: evaluate result is nil in main execution context")
 	}
 
 	f.documentHandle = result.(*ElementHandle)