phase 2 removing tbc

Strip dead pfUI.client > 11200 and pfUI.expansion == "tbc" branches now
that vanilla is the only supported client.

- pfUI.lua: hardcode expansion = "vanilla"; collapse force_region matrix
- compat/vanilla.lua, libs/{libcast,libdebuff,libtotem,libunitscan,
  focus}: drop always-false early-returns
- api/unitframes.lua: delete TargetBuffOnUpdate poller + tbc visibility
  and secure-template branches; click-cast keeps only vanilla path
- api/ui-widgets.lua: unconditional EffectiveScale divide
- env/tables.lua: drop unused focus/focustarget pfValidUnits entries
- modules/actionbar.lua: simplify EnablePaging, drop ButtonSwitch/
  petvisibility, unwrap prowl block, single keybind-remap path
- modules/{castbar,chat,cooldown,loot,questitem,totems}: unwrap
  always-true conditionals
- modules/nameplates.lua: cfg-only fake-cooldown gate, unwrap overlap/
  clickthrough + mouselook blocks
- modules/friends.lua + skins/blizzard/friends.lua: maxtab = 4
- skins/blizzard/{help,game_menu,questlog}: drop tbc-only branches

modules/cooldown.lua

@@ -134,14 +134,7 @@ pfUI:RegisterModule("cooldown", "vanilla:tbc", function ()
     end
   end
 
-  if pfUI.expansion == "vanilla" then
-    -- vanilla does not have a cooldown frame type, so we hook the
-    -- regular SetTimer function that each one is calling.
-    hooksecurefunc("CooldownFrame_SetTimer", SetCooldown)
-  else
-    -- tbc and later expansion have a cooldown frametype, so we can
-    -- hook directly into the frame creation and add our function there.
-    local methods = getmetatable(CreateFrame('Cooldown', nil, nil, 'CooldownFrameTemplate')).__index
-    hooksecurefunc(methods, 'SetCooldown', SetCooldown)
-  end
+  -- vanilla does not have a cooldown frame type, so we hook the
+  -- regular SetTimer function that each one is calling.
+  hooksecurefunc("CooldownFrame_SetTimer", SetCooldown)
 end)