Return value of `_wp_delete_all_temp_backups()` isn't used

[johnbillion]

The _wp_delete_all_temp_backups() function returns a WP_Error object when there's a failure condition, but this function is only used as a cron event callback function so the return value is not used anywhere.

As core has no error handling for cron events, I recommend triggering an error for these conditions (probably via wp_trigger_error()) and then doing early returns so the function returns void.

[johnbillion]

Correction: This function is used as a shutdown action callback (​ref), not a cron event callback. Same problem though.

[amitraj2203]

Patch file.

[amitraj2203]

Hi @johnbillion I have submitted the patch for the same.

Trac ticket: https://core.trac.wordpress.org/ticket/61116

[SergeyBiryukov]

In 58906:

Upgrade/Install: Remove the return value of _wp_delete_all_temp_backups().

This function is only utilized as a shutdown action callback, so the return value is not used anywhere.

wp_trigger_error() is now used instead under the same conditions.

Follow-up to [55720], [56342].

Props johnbillion, amitraj2203, narenin.
Fixes #61116.

Thanks for the PR! Merged in r58906.