gui/views: Fix event margins in week header

Margins are already applied to the event widget itself through CSS.
This commit removes unnecessary margins and row spacing to bring
it in line with the month view.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-calendar/-/merge_requests/649>

src/gui/views/gcal-week-header.blp

@@ -38,9 +38,6 @@ template $GcalWeekHeader: Widget {
           Grid grid {
             column-homogeneous: true;
             hexpand: true;
-            column-spacing: 6;
-            row-spacing: 2;
-            margin-start: 6;
           }
         }
       }

src/gui/views/gcal-week-header.c

@@ -242,7 +242,6 @@ static inline void
 setup_event_widget (GcalWeekHeader *self,
                     GtkWidget      *widget)
 {
-  gtk_widget_set_margin_end (widget, 6);
   g_signal_connect_object (widget, "activate", G_CALLBACK (on_event_widget_activated), self, 0);
 }