Fix tilt laser mux topic for obstacle observation

[YutoUchimi]

Part of #407

ground_object_cloud is disabled in PR1040's current working branch of jsk_robot (jsk-ros-pkg/jsk_robot#1143), so the topic name must be fixed.

[http://pr1040:11311][133.11.216.144] yuto@yuto-ThinkPad-T460s:~
$ rosservice call /tilt_laser_mux/list
topics: ['/tilt_scan_filtered', '/empty_cloud']
[http://pr1040:11311][133.11.216.144] yuto@yuto-ThinkPad-T460s:~
$ rosservice call /tilt_laser_mux/select "ground_object_cloud"
ERROR: service [/tilt_laser_mux/select] responded with an error: 
[http://pr1040:11311][133.11.216.144] yuto@yuto-ThinkPad-T460s:~
$ rostopic echo -n1 /tilt_laser_mux/selected 
data: tilt_scan_filtered
---

[k-okada]

ground_object_cloud is disabled in PR1040 how about pr1012?

[YutoUchimi]

Also disabled in PR1012.

[http://pr1012:11311][133.11.216.119] yutouchimi@libra:~
$ rosservice call /tilt_laser_mux/list 
topics: [/empty_cloud, /tilt_scan_filtered]
[http://pr1012:11311][133.11.216.119] yutouchimi@libra:~
$ rostopic list | grep ground
[http://pr1012:11311][133.11.216.119] yutouchimi@libra:~
$