ANDROID: Remove CPU hotplug support from microdroid

Microdroid doesn't have a need to be able to hotplug CPUs, so remove
support for it.

Bug: 432329937
Change-Id: Iec229e80d60024612ce2f2fed091c51a2773782d
Signed-off-by: Isaac J. Manjarres <isaacmanjarres@google.com>