Tools: remove RELY from undocumented message greylist

.... as it is now documented

Author: peterbarker

Tools/autotest/vehicle_test_suite.py

@@ -3100,7 +3100,6 @@ def LoggerDocumentation_greylist(self):
             "IREG",  # INS something
             "ISBD",  # InertialSensor batch logging
             "ISBH",  # InertialSensor batch logging
-            "RELY",  # relay
             "RTCM",  # GPS
             "SBRE",  # septentrio