Fix #148004: Dope Sheet editor playback controls are off by default

Enable the Playback Controls (footer region) by default in the Dope Sheet
editors.

Pull Request: https://projects.blender.org/blender/blender/pulls/148008

source/blender/editors/space_action/space_action.cc

@@ -87,7 +87,6 @@ static SpaceLink *action_create(const ScrArea *area, const Scene *scene)
   BLI_addtail(&saction->regionbase, region);
   region->regiontype = RGN_TYPE_FOOTER;
   region->alignment = (U.uiflag & USER_HEADER_BOTTOM) ? RGN_ALIGN_TOP : RGN_ALIGN_BOTTOM;
-  region->flag = RGN_FLAG_HIDDEN;
 
   /* channel list region */
   region = BKE_area_region_new();