Mentioning the internal random file name is useless because none of us have administrator access to the site database.
But, you, as owner of question 306290/in-a-libreoffice-writer-document-the-hyperlinks-work-ok-but-the-cursor-does-not-change-to-a-hand-pointer-when-hovered-over-the-link, can edit it and remove the link to the uploaded file.
There is no guarantee that the file will be effectively erased but no public link will point to it.
This may not disable plagiarism check because many search engines (like Google) also use a history cache to hit on deleted/removed content.
This is why we always recommend, when data is private or sensitive, to always sanitize it before uploading. One of the traditional method is to replace real text with “lorem ipsum”, of course provided this doesn’t remove the problem too.
EDIT
Following @mikekaganski’s comment: also make sure “Track changes” is disabled and File
>Save as
to make sure no “fossil” remains hidden.
To show the community your question has been answered, click the ✓ next to the correct answer, and “upvote” by clicking on the ^ arrow of any helpful answers. These are the mechanisms for communicating the quality of the Q&A on this site. Thanks!