AC_AutoTune: fixed testing of gains with aux switch

this fixes the use of an aux switch for autotune to test gains before
disarm.

Many thanks to Mark Whitehorn for noticing this regression

libraries/AC_AutoTune/AC_AutoTune.cpp

@@ -190,8 +190,6 @@ bool AC_AutoTune::init_internals(bool _use_poshold,
 // stop - should be called when the ch7/ch8 switch is switched OFF
 void AC_AutoTune::stop()
 {
-    axes_completed = 0;
-
     // set gains to their original values
     load_gains(GAIN_ORIGINAL);