One removed SimplePie file was not added to `$_old_files` in WP 6.9

[WFMattR]

When updating a site from 6.8.3 to 6.9, wp-includes/SimplePie/src/Decode and its subdirs and contained file were correctly removed, but wp-includes/SimplePie/src/Core.php still remains.

The $_old_files array was updated in trac ticket #64320. Core.php was mentioned in the list at the top of the ticket, but it looks like it was just missed in the array.

Added wp-includes/SimplePie/src/Core.php file to the $_old_files array.

Trac ticket: https://core.trac.wordpress.org/ticket/64336

[mukesh27]

Is there anything we should take care of before the general release? Do we need to document this somewhere so we can address it before the release?

[SergeyBiryukov]

In 61351:

Upgrade/Install: Add missing file to the $_old_files array.

Follow-up to [60490], [61338].

Props WFMattR, sajib1223, davidbaumwald, mukesh27, SergeyBiryukov.
Fixes #64336.

[SergeyBiryukov]

Reopening for backporting to the 6.9 branch.

[desrosj]

Replying to mukesh27:

Is there anything we should take care of before the general release? Do we need to document this somewhere so we can address it before the release?

@mukesh27 I'm not sure what you mean here. Could you clarify? I think what you're asking is if the release checklists need to be updated to make sure this is not missed next time. Is that right?

[61351] looks good to backport.

[peterwilsoncc]

In 61383:

Upgrade/Install: Add missing file to the $_old_files array.

Follow-up to [60490], [61338].

Reviewed by desrosj.
Merges [61351] to the 6.9 branch.

Props WFMattR, sajib1223, davidbaumwald, mukesh27, SergeyBiryukov.
Fixes #64336.