Orphan Image/File When Cancel Submit Job

#### Steps to Reproduce
1. On submit job form upload image (e.g Logo)
2. Because of AJAX upload, this will upload image even when user did not submit the form.
3. Do not submit the form.
4. The file is still in upload folder. Not even attached/an attachment.
5. Just there. with no purpose and no way to clean them up.

#### What I Expected
Removed or not uploaded at all. Maybe use File Reader JS (but it have some cons compared to AJAX upload), etc,

#### What Happened Instead
Just there. with no purpose and no way to clean them up.

#### WordPress / WP Job Manager Version
WP 4.9/1.29.2

#### Browser / OS Version

#### Screenshot / Video

#### Context / Source

Start by tracing the submit-job form's AJAX upload flow and the upload-folder or attachment handling described in the report. Reproduce the upload-then-cancel sequence; done means an abandoned file is removed or never persists, while a submitted image remains available.

Written by the indexing model from the issue text.