This leaves only the lambda/std::function based CallbackQueue2, soon to be renamed just CallbackQueue. Issue-on: https://gem5.atlassian.net/browse/GEM5-698 Change-Id: I4e2fd3b7b684c414be6db0e268284ab63e6cfdff Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/32650 Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com> Reviewed-by: Jason Lowe-Power <power.jg@gmail.com> Maintainer: Jason Lowe-Power <power.jg@gmail.com> Tested-by: kokoro <noreply+kokoro@google.com>