Fix voxel grid update when robot base moves

While the costmap is correct, the underlying voxel grid ends up being incorrect when the robot moves as the underlying voxel_grid is not cleared out prior to copying the data back into the new location.

I went back through the history, and found https://github.com/ros-planning/navigation/commit/b6d26e8e14051b1073619d2f1ef1b6b66025053a, which shows that resetMaps used to also clear the voxel_grid_ prior to plugin re-write.

I do need to test this fully to make sure that it doesn't cause issues (note the deactivate/activate wrapped around reset() function right above it), but wanted to open a PR so I could put in this extra information and links.