Remove unused robot_radius parameter

@mikeferguson can you confirm this? Looking at the code and experimenting without it, it seems this parameter is unused. Perhaps this was made redundant by the `robot_radius` parameter now in [Costmap2D.cfg](https://github.com/ros-planning/navigation/blob/88e802d89a28d5dbee0ce10ab3c0ab1931830e30/costmap_2d/cfg/Costmap2D.cfg#L20).

For further discussion, see https://github.com/turtlebot/turtlebot_apps/issues/94.
Merge pull request #209 from stonier/patch-1

Remove unused robot_radius parameter
renames acc_lim_th to acc_lim_theta
Merge pull request #212 from efernandez/acc_lim_theta

renames acc_lim_th to acc_lim_theta
restore acc_lim_th with warning
uncommented line in global_planner that pushes the goal onto the end of the global path and switched move_base's planService to search in a widening circle up to the given tolerance
Merge branch 'hydro-devel' of https://github.com/ros-planning/navigation into add_goal_to_path
Merge branch 'add_goal_to_path' of https://github.com/KaijenHsiao/navigation into add_goal_to_path