Fix closing the filestream and deleting the fragment

[pereirinha]

Fixes the removal of unnecessary fragments.

Approach

• Fixes the closing of the file stream;
• Fixes the function to delete the file from the file system

QA notes

• Download an asset from Cloudinary DAM into WordPress;
• Visit the temp folder — usually /var/tmp/ or /tmp/;
• Confirm that there isn't a file with the following pattern:
  • Original filename: image.jpg;
  • Temporary file: image-XsWqIe.tmp — filename suffixed with 6 random chars and the file extension tmp.