AC_AutoTune: fix restoring of original gains

current_gain_type was not being set when load_gains was called meaning subsequent calls to load_gains would fail if gain_type was GAIN_ORIGINAL

libraries/AC_AutoTune/AC_AutoTune.cpp

@@ -907,7 +907,6 @@ void AC_AutoTune::backup_gains_and_initialise()
     // no axes are complete
     axes_completed = 0;
 
-    current_gain_type = GAIN_ORIGINAL;
     positive_direction = false;
     step = WAITING_FOR_LEVEL;
     step_start_time_ms = AP_HAL::millis();
@@ -1104,9 +1103,6 @@ void AC_AutoTune::load_twitch_gains()
  */
 void AC_AutoTune::load_gains(enum GainType gain_type)
 {
-    if (current_gain_type == gain_type) {
-        return;
-    }
     switch (gain_type) {
     case GAIN_ORIGINAL:
         load_orig_gains();

libraries/AC_AutoTune/AC_AutoTune.h

@@ -170,7 +170,6 @@ private:
         GAIN_INTRA_TEST = 2,
         GAIN_TUNED      = 3,
     };
-    enum GainType current_gain_type;
     void load_gains(enum GainType gain_type);
 
     TuneMode mode                : 2;    // see TuneMode for what modes are allowed