Remove system_path from DiskInfo in cros-disks client

GetDeviceProperties() in cros-disks returns information about a device.
One of the fields, called |NativePath| in the D-Bus API, and
|system_drive| in chromeos::disks, is not used. Considering the value is
used as the parameter to lookup a drive in GetDeviceProperties(), ignore
the field in the client as the client already knows the value.

Bug: 961181
Change-Id: If667c35e806689badcc66bacf450b6f92c7cda52
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1602238
Reviewed-by: Anand Mistry <amistry@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Austin Tankiang <austinct@chromium.org>
Cr-Commit-Position: refs/heads/master@{#660235}
9 files changed