Remove PCI hotplug core MAINTAINERS entry

Per discussion w/Kristen at the LPC PCI BoF, the core hotplug code doesn't
really need a separate maintainer, so remove the entry (but leave the driver
specific ones).

Signed-off-by: Kristen Carlson Accardi <kristen.c.accardi@intel.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>