[robotiq_ft_sensor] Delete _gencfg dependency

[Michi-Tsubaki]

Currently, when building robotiq_ft_sensor, the following errors occur.

CMake Error at CMakeLists.txt:50 (add_dependencies):
  The dependency target "robotiq_ft_sensor_gencfg" of target "rq_sensor" does
  not exist.


CMake Error at CMakeLists.txt:54 (add_dependencies):
  The dependency target "robotiq_ft_sensor_gencfg" of target "rq_test_sensor"
  does not exist.

This package seems not to use dynamic_reconfigure, so *_gencfg are not needed.

This PR delete the dependency of "robotiq_ft_sensor_gencfg" to succeed in building the package.

If you/users want to use dynamic_reconfigure, you should add <depend>dynamic_reconfigure</depend> in stead of deleting this dependency.