phase 3 removing tbc

Drop the now-vestigial expansion plumbing.

- Delete modules/thirdparty-tbc.lua + its xml Include
- Strip 10 tbc-tagged CreateConfig calls in modules/gui.lua
- Drop the expansion arg from CreateConfig() signature + the disabled-
  entry rendering path that depended on it
- Drop the showdisabled GUI toggle + its default
- Simplify pfUI:RegisterModule / pfUI:RegisterSkin to (name, func) only
- Strip the leading version arg ("vanilla:tbc", etc.) from all 114
  Register call sites
- Delete the pfUI.expansion variable

modules/turtle-wow.lua

@@ -1,7 +1,7 @@
 -- skip module initialization on every other client than turtle-wow
 if not TargetHPText or not TargetHPPercText then return end
 
-pfUI:RegisterModule("turtle-wow", "vanilla", function ()
+pfUI:RegisterModule("turtle-wow", function ()
   -- Manage Turtle WoW's GroupUI (Turtle_GroupUI addon) vs pfUI frames.
   --
   -- Turtle uses GroupClusterFrame1-8 for BOTH party AND raid display,