utils: Pass GcalCalendar to ask_recurrence_modification_type()

The method ask_recurrence_modification_type() currently
receives an ESource, and tried to fetch the ECalClient
from the ESource by using g_object_get_data().

However, since we moved to GcalCalendar, we do not set
this data field in ESource.

Receive a GcalCalendar instead, and use the appropriate
function gcal_calendar_get_client() instead.

src/views/gcal-month-cell.c

@@ -209,7 +209,6 @@ gcal_month_cell_drag_drop (GtkWidget      *widget,
   GtkWidget *event_widget;
   GDateTime *start_dt, *end_dt;
   GcalEvent *event;
-  ESource *source;
   gint diff;
   gint start_month, current_month;
   gint start_year, current_year;
@@ -227,10 +226,9 @@ gcal_month_cell_drag_drop (GtkWidget      *widget,
 
   event = gcal_event_widget_get_event (GCAL_EVENT_WIDGET (event_widget));
   calendar = gcal_event_get_calendar (event);
-  source = gcal_calendar_get_source (calendar);
 
   if (gcal_event_has_recurrence (event) &&
-      !ask_recurrence_modification_type (widget, &mod, source))
+      !ask_recurrence_modification_type (widget, &mod, calendar))
     {
       goto out;
     }

src/views/gcal-week-grid.c

@@ -981,7 +981,6 @@ gcal_week_grid_drag_drop (GtkWidget      *widget,
   GcalCalendar *calendar;
   GtkWidget *event_widget;
   GcalEvent *event;
-  ESource *source;
   GTimeSpan timespan = 0;
   gboolean ltr;
   gint drop_cell;
@@ -1012,10 +1011,9 @@ gcal_week_grid_drag_drop (GtkWidget      *widget,
 
   event = gcal_event_widget_get_event (GCAL_EVENT_WIDGET (event_widget));
   calendar = gcal_event_get_calendar (event);
-  source = gcal_calendar_get_source (calendar);
 
   if (gcal_event_has_recurrence (event) &&
-      !ask_recurrence_modification_type (widget, &mod, source))
+      !ask_recurrence_modification_type (widget, &mod, calendar))
     {
       goto out;
     }

src/views/gcal-year-view.c

@@ -1515,16 +1515,14 @@ navigator_drag_drop_cb (GcalYearView   *self,
           GcalEvent *event;
           GDateTime *start_dt, *end_dt;
           GDateTime *drop_date;
-          ESource *source;
 
           event_widget = GCAL_EVENT_WIDGET (gtk_drag_get_source_widget (context));
           event = gcal_event_widget_get_event (event_widget);
           calendar = gcal_event_get_calendar (event);
-          source = gcal_calendar_get_source (calendar);
           mod = GCAL_RECURRENCE_MOD_THIS_ONLY;
 
           if (gcal_event_has_recurrence (event) &&
-              !ask_recurrence_modification_type (GTK_WIDGET (self), &mod, source))
+              !ask_recurrence_modification_type (GTK_WIDGET (self), &mod, calendar))
             {
               goto out;
             }