message: remove visual representation of virtual SDH grasp and tip links
diff: <child link="${name}_grasp_link" />
  </joint>
  - <link name="${name}_grasp_link">
  - <xacro:default_inertial/>
  - <visual>
  - <origin xyz="0 0 0" rpy="0 0 0" />
  - <geometry>
  - <box size="0.001 0.001 0.001" />
  - </geometry>
  - </visual>
  - <collision>
  - <origin xyz="0 0 0" rpy="0 0 0" />
  - <geometry>
  - <box size="0.001 0.001 0.001" />
  - </geometry>
  - </collision>
  - </link>
  + <link name="${name}_grasp_link" />
  <!-- tip link -->
  <joint name="${name}_tip_joint" type="fixed" >
  <child link="${name}_tip_link" />
  </joint>
  - <link name="${name}_tip_link">
  - <xacro:default_inertial/>
  - <visual>
  - <origin xyz="0 0 0" rpy="0 0 0" />
  - <geometry>
  - <box size="0.001 0.001 0.001" />
  - </geometry>
  - </visual>
  - <collision>
  - <origin xyz="0 0 0" rpy="0 0 0" />
  - <geometry>
  - <box size="0.001 0.001 0.001" />
  - </geometry>
  - </collision>
  - </link>
  + <link name="${name}_tip_link" />
  <!-- finger1 -->
  <!-- joint between sdh_palm_link and sdh_finger_11_link -->
  