Remove redundant estep rate code from LIN_ADVANCE

As noted by https://github.com/MarlinFirmware/Marlin/pull/4971#issuecomment-252503295

Marlin/stepper.cpp

 
     #if ENABLED(LIN_ADVANCE)
 
-      if (current_block->use_advance_lead)
-        current_estep_rate[TOOL_E_INDEX] = ((uint32_t)acc_step_rate * current_block->e_speed_multiplier8) >> 8;
-
       if (current_block->use_advance_lead) {
         #if ENABLED(MIXING_EXTRUDER)
           MIXING_STEPPERS_LOOP(j)