cpu: Remove the ancient do_quiesce config option.

cpu: Remove the ancient do_quiesce config option.

This option has existed for a very long time, defaults to True, and is
not used in any of the checked in configs. It enables the "quiesce"
mechanism, originally just pseudo instructions, and it's not clear
why you'd ever want to turn it off.

Change-Id: I92c7e5af22157e8435c7326634857d30bb5d7254
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/25143
Reviewed-by: Anthony Gutierrez <anthony.gutierrez@amd.com>
Reviewed-by: Matthew Poremba <matthew.poremba@amd.com>
Maintainer: Anthony Gutierrez <anthony.gutierrez@amd.com>
Tested-by: kokoro <noreply+kokoro@google.com>