add simplify_file to remove some redundant fields from uploaded file object

coretool.js

@@ -351,4 +351,14 @@ module.exports = {
     return arr.reduce((obj, item) => ({ ...obj, [item[key]]: item }), {})
   },
 
+  simplify_file (file = {}) {
+    delete file.baseUrl
+    delete file.fileUrl
+    delete file.ipfsUrl
+    delete file.fieldname
+    delete file.filename
+    delete file.destination
+    return file
+  }
+
 }