katana_gazebo_plugins: replace deprecated function calls
katana_gazebo_plugins: remove unused constant
katana_gazebo_plugins: don't update controller gains in each timestep

The problem was that starting with Hydro, control_toolbox supports
dynamic_reconfigure. That means there is a certain overhead (log
entries, cpu) whenever setGains() is called. Previously, it was called
in each simulation cycle, which was unnecessary anyway. This commit
fixes that.

* avoids gigabytes of log output
* speeds up simulation by a factor of 3-4
* fixes #7