PCI/PME: Drop unused support for PMEs from Root Complex Event Collectors

Since we register pcie_pme_driver only for PCI_EXP_TYPE_ROOT_PORT, the PME
driver never claims Root Complex Event Collectors.

Remove unused code related to Root Complex Event Collectors.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>