Remove the redundant Simulink telemetry in hexapod. This ticket will need to modify the Simulink model, low-level controller code, and EUI.

1. Rename "MFDFrac" to "MJDFrac"
2. Remove "TrackMode"
3. Remove "LinearEncoder1" to "LinearEncoder6"
4. Remove "LinearEncoderVelocity1" to "LinearEncoderVelocity6"
5. Rename "CommandPos_n", "CommandVel_n", and "CommandAccel_n " to "DemandPos_n", "DemandVel_n", and "DemandAccel_n"

For 4, check with Felipe that we could get the velocity from encoder or not. Right now, the value is estimated by the Simulink model ("EstVel_1" to "EstVel_6").