Resolves issue OpenSimulationInterface#306 (OpenSimulationInterface#378)

- Removed incorrect rule due to misinterpretation of "absolute"
- Improved comment

Author: jdsika

osi_featuredata.proto

@@ -291,14 +291,10 @@ message RadarDetection
     //
     optional Spherical3d position_rmse = 4;
 
-    // Absolute radial (in direction to the sensor) velocity of the detection.
+    // Radial velocity of the detection positive in direction to the sensor.
     //
     // Unit: m/s
     //
-    // \rules
-    // is_greater_than_or_equal_to: 0
-    // \endrules
-    //
     optional double radial_velocity = 5;
 
     // Root mean squared error of the object measured radial velocity.