app: remove the "Save" button from the "Configure Keyboard Shortcuts" dialog.

This was always confusing to people that they had to click "Save" then "Close".
With new code anyway, any change is instantly put into effect, and the only
point of "Save" is to actually store immediately in the shortcutsrc file. But
this is clearly not very clear to people (and it can be done in the Preferences
dialog too).

Instead let's just have a "OK" button. The file will be actually updated on exit
only (if "Save keyboard shortcuts on exit" is checked). And that's it.

The only missing feature would be the ability to cancel the latest changes
before hitting OK, i.e. having a "Cancel" button too. Let's see to do this
later.

app/dialogs/keyboard-shortcuts-dialog.c

@@ -36,9 +36,6 @@
 #include "gimp-intl.h"
 
 
-#define RESPONSE_SAVE 1
-
-
 /*  local function prototypes  */
 
 static void   keyboard_shortcuts_dialog_response (GtkWidget *dialog,
@@ -65,8 +62,7 @@ keyboard_shortcuts_dialog_new (Gimp *gimp)
                             gimp_standard_help_func,
                             GIMP_HELP_KEYBOARD_SHORTCUTS,
 
-                            _("_Save"),  RESPONSE_SAVE,
-                            _("_Close"), GTK_RESPONSE_CLOSE,
+                            _("_OK"), GTK_RESPONSE_OK,
 
                             NULL);
 
@@ -108,10 +104,6 @@ keyboard_shortcuts_dialog_response (GtkWidget *dialog,
 {
   switch (response)
     {
-    case RESPONSE_SAVE:
-      menus_save (gimp, TRUE);
-      break;
-
     default:
       gtk_widget_destroy (dialog);
       break;