arch: Delete the unused ProcessInfo class.

arch: Delete the unused ProcessInfo class.

Change-Id: Ie67f696005fa60e117e1e4e4e985aee5e767ccec
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/30958
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>