Does delete_post_thumbnail() actually delete the image?

No it certainly doesn’t. It is simply a case of poor choice of naming. The function should have been named unset_post_thumbnail(), particularly when we already have set_post_thumbnail().

Today’s WordPress annoyance.

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)