This OO.ui.infuse is not used: ext.abuseFilter.edit.js#563. Additionally, the #wpFilterDeletedLabel element doesn't seem to exist: Code search. (Edit: the element exists actually, see messages below.)
Introduced in these changes, I guess it's an oversight. Just in case, ping @Daimona.
Change #1083492 had a related patch set uploaded (by Gerrit Patch Uploader; author: Anne Haunime):
[mediawiki/extensions/AbuseFilter@master] Clean up an OOUI infuse that is unused and on a nonexisting element
Actually, the #wpFilterDeletedLabel element does exist. Otherwise, the infuse would produce a JavaScript error.
It is a container of the #wpFilterDeleted checkbox. I have no idea how come it is generated.
The #wpFilterDeleted and #wpFilterDeletedLabel elements are created (amongst the other ones) in this loop: AbuseFilterViewEdit.php#456.
I would suggest to add code comments to allow to grep for them, as it is already done for abusefilter-edit-enabled, etc. and isEnabled(), etc.
Change #1083958 had a related patch set uploaded (by Gerrit Patch Uploader; author: Anne Haunime):
[mediawiki/extensions/AbuseFilter@master] Add code comments to help find dynamically-generated IDs in the codebase
Change #1083958 merged by jenkins-bot:
[mediawiki/extensions/AbuseFilter@master] Add code comments to help find dynamically-generated IDs in the codebase
Change #1083492 merged by jenkins-bot:
[mediawiki/extensions/AbuseFilter@master] Clean up an unused OOUI infuse