This isn't a bug for each wiki because I didn't want to spam everybody by creating 15 new bugs.
I did a quick check through the wikis listed on https://noc.wikimedia.org/conf/dblists/private.dblist (it's generally quite easy to guess what the URL for each database name is, but https://git.wikimedia.org/blob/operations%2Fmediawiki-config.git/HEAD/wmf-config%2FInitialiseSettings.php#L1135 is a good reference otherwise)
The following wikis are using the CC footer:
- ilwikimedia (chapter)
- searchcomwiki (closed)
- spcomwiki (closed)
The following private wikis don't seem to agree on exactly what text to use:
- checkuserwiki has "Content is copyrighted (© all rights reserved) by the Wikimedia Foundation"
- collabwiki has "Unless otherwise noted, text is copyright Wikimedia Foundation and may not be distributed or used without permission. Additional terms may apply."
- internalwiki has "Content is copyrighted by the Wikimedia Foundation"
- legalteamwiki has "This wiki is private, and subject to your professional and employee confidentiality obligations. Where confidentiality obligations do not apply, material in the wiki is available under CC BY-SA 3.0."
- officewiki has "The contents of this Office Wiki are confidential. Only users that have signed the Wikimedia Foundation's Confidentiality Agreement are authorized to have access."
- stewardwiki has "Content is copyrighted (© all rights reserved) by the Wikimedia Foundation."
I think the remaining 5 private wikis have no text.