Fix changelog

Author: Myzhar

CHANGELOG.rst

@@ -77,7 +77,6 @@ v5.1.0
   - Added parameter `pos_tracking.publish_3d_landmarks` to enable/disable landmarks publishing
   - Added parameter `pos_tracking.publish_lm_skip_frame` to set the frequency of landmarks publishing (0 to publish every frame)
 
-- Changed the default positional tracking mode from `GEN_1` to `GEN_3`
 - Removed Point Cloud Transport as a required dependency. Point Cloud Transport is now only automatically enabled if the `point_cloud_transport` package is installed on the system.
 - Removed FFMPEG Image Transport support because of a problem with the Humble distribution not allowing to set the transport parameters, and the lack of compatibility with NVIDIA® Jetson.
 - Improved diagnostic information for 3D Mapping status in diagnostics