libxl: do not remove unidentified frontend paths in libxl__devices_destroy
Currently this appears to only include "/local/domain/<domid>/device/suspend".
Ultimately the caller will nuke the whole guest directory anyway but not having
this function remove things which don't look like devices seems less
surprising.
Signed-off-by: Ian Campbell <ian.campbell@citrix.com> Acked-by: Ian Jackson <ian.jackson.citrix.com> Committed-by: Ian Jackson <ian.jackson.citrix.com>