Update commentary on M48

Marlin/Marlin_main.cpp

    *     L = Number of legs of movement before probe
    *     S = Schizoid (Or Star if you prefer)
    *
-   * This function assumes the bed has been homed.  Specifically, that a G28 command
-   * as been issued prior to invoking the M48 Z probe repeatability measurement function.
-   * Any information generated by a prior G29 Bed leveling command will be lost and need to be
-   * regenerated.
+   * This function requires the machine to be homed before invocation.
    */
   inline void gcode_M48() {