calc-sun: Prefer g_auto* macros

g_autofree will automatically free variables when they go out of
scope. g_autoptr will do the same, but using the appropriate freefunc
for the given type, e.g. GDateTime -> g_date_time_unref() or
GObject -> g_object_unref().

This automatic cleanup reduces the risk of memory leaks
and allows getting rid of some lines of code.

src/calculations/calculations_sun.c

@@ -64,7 +64,7 @@ double
                                  double     latitude)
 {
   double siderial_time;
-  double *coordinates_sun;
+  g_autofree double *coordinates_sun = NULL;
   double *coordinates_horizontal_sun;
 
 
@@ -73,7 +73,6 @@ double
   coordinates_horizontal_sun = picplanner_transform_rotational_to_horizontal (coordinates_sun,
                                                                               latitude,
                                                                               siderial_time);
-  g_free (coordinates_sun);
 
   return coordinates_horizontal_sun;
 }
@@ -84,23 +83,18 @@ double
                                        double     longitude,
                                        double     latitude)
 {
-  GDateTime *iteration_time;
-  double *coordinates_sun;
   double *array_coordinates_sun = malloc (sizeof (double) * 2 * NUM_DATA_POINTS);
 
   for (int i=0; i<NUM_DATA_POINTS; i++)
     {
-      iteration_time = g_date_time_add_minutes (date_time, i*24*60/NUM_DATA_POINTS-12*60);
-
-      coordinates_sun = picplanner_get_coordinates_sun (iteration_time,
-                                                        longitude,
-                                                        latitude);
+      GDateTime *iteration_time = g_date_time_add_minutes (date_time, i*24*60/NUM_DATA_POINTS-12*60);
+      g_autofree double *coordinates_sun =
+	picplanner_get_coordinates_sun (iteration_time,
+					longitude,
+					latitude);
 
       array_coordinates_sun[2*i] = coordinates_sun[0];
       array_coordinates_sun[2*i+1] = coordinates_sun[1];
-
-      g_free (coordinates_sun);
-      g_date_time_unref (iteration_time);
     }
 
   return array_coordinates_sun;