sys: Bump GIANT device removal to 16.0

It did not happen prior to FreeBSD 15.0.

Approved by: re (cperciva)
Reported by: zlei
Sponsored by: The FreeBSD Foundation

(cherry picked from commit 24adb135c5fe8d5018781d496e0abae914534ce5)
(cherry picked from commit 8e276f22bd5dc43799e3b32e55326aca3fa10a54)