Cloud Storage: fix bug that does not allow deleting multiple Google Drive backups

[montoner0]

Description
When ESGST tries to remove multiple backup files from Google Drive it throws Unknown Error. Same error for auto and manual removal. Same files can be successfully removed one-by-one.

Steps to Reproduce

1. Go to "Restore data"
2. Click on "Restore from: Google Drive"
3. Select several files
4. Click on "Delete selected files" and confirm removal
5. Get "Unknown error" message

Expected Behavior
Files should be deleted without errors.

Console Errors
Request URL:https://www.googleapis.com/batch/drive/v3
Request method:POST
Remote address:216.58.211.138:443
Status code:500
Version:HTTP/2

Screenshots

System (please complete the following information):

• ESGST Version: Extension v8.5.12
• Browser + Version: Firefox v73