Mac: Use IOKit IOService:/ paths for devices

Change hid_enumerate() and hid_open_path() to use IOKit IOService:/
paths to uniquely identify devices, instead of creating a path
(done by the make_path() function).

The path passed to hid_open_path() now must be a valid path to an
IOHIDDevice in the IOService plane, like:
"IOService:/AppleACPIPlatformExpert/PCI0@0/AppleACPIPCI/EHC1@1D,7/
AppleUSBEHCI/PLAYSTATION(R)3
Controller@fd120000/IOUSBInterface@0/IOUSBHIDDriver"
Mac: Remove unused get_string_property_utf8()

Remove get_string_property_utf8(), it's not used since make_path() was removed
Mac: Disable unused get_location_id()

Disable get_location_id(), it's not used in active code since make_path() was removed