app: queue a draw on the canvas in gimp_canvas_set_bg_color()

Instead of doing it in gimp_display_shell_set_padding() from where
it's called.

app/display/gimpcanvas.c

@@ -301,4 +301,6 @@ gimp_canvas_set_bg_color (GimpCanvas *canvas,
   gdk_colormap_alloc_color (colormap, &gdk_color, FALSE, TRUE);
 
   gdk_window_set_background (gtk_widget_get_window (widget), &gdk_color);
+
+  gtk_widget_queue_draw (GTK_WIDGET (canvas));
 }

app/display/gimpdisplayshell-appearance.c

@@ -41,7 +41,6 @@
 #include "gimpdisplay.h"
 #include "gimpdisplayshell.h"
 #include "gimpdisplayshell-appearance.h"
-#include "gimpdisplayshell-expose.h"
 #include "gimpdisplayshell-selection.h"
 #include "gimpimagewindow.h"
 #include "gimpstatusbar.h"
@@ -502,8 +501,6 @@ gimp_display_shell_set_padding (GimpDisplayShell      *shell,
 
   appearance_set_action_color (shell, "view-padding-color-menu",
                                &options->padding_color);
-
-  gimp_display_shell_expose_full (shell);
 }
 
 void