common.xml: update OF field descriptions to point out deprecation

message_definitions/v1.0/common.xml

@@ -4914,8 +4914,8 @@
       <description>Optical flow from a flow sensor (e.g. optical mouse sensor)</description>
       <field type="uint64_t" name="time_usec" units="us">Timestamp (UNIX Epoch time or time since system boot). The receiving end can infer timestamp format (since 1.1.1970 or since system boot) by checking for the magnitude of the number.</field>
       <field type="uint8_t" name="sensor_id">Sensor ID</field>
-      <field type="int16_t" name="flow_x" units="dpix">Flow in x-sensor direction</field>
-      <field type="int16_t" name="flow_y" units="dpix">Flow in y-sensor direction</field>
+      <field type="int16_t" name="flow_x" units="rad/s">Flow rate around X-axis (deprecated; use flow_rate_x)</field>
+      <field type="int16_t" name="flow_y" units="rad/s">Flow rate around Y-axis (deprecated; use flow_rate_y)</field>
       <field type="float" name="flow_comp_m_x" units="m/s">Flow in x-sensor direction, angular-speed compensated</field>
       <field type="float" name="flow_comp_m_y" units="m/s">Flow in y-sensor direction, angular-speed compensated</field>
       <field type="uint8_t" name="quality">Optical flow quality / confidence. 0: bad, 255: maximum quality</field>