mouseover/libpredict: drop legacy spell-target plumbing

With Nampower as a hard dep, /pfcast for spell names always takes the
early CastSpellByName(msg, unit) path. The fallback branch that did the
SpellTargetUnit dance (resolve a friendly unit token, disable AutoSelf
Cast, call SpellTargetUnit) hasn't been reachable in a while, and it
dragged a pile of supporting infrastructure with it.

modules/mouseover.lua:
- Drop the st_units token list, GetUnitString helper, and the
  UnitTokenFromGUID rewrite of GetUnitString — all only used by the
  dead fallback.
- Drop the NoSelfCast helper (only the dead fallback called it).
- Drop the pfMouseOver frame; its only purpose was to hold a .unit
  field the dead fallback wrote and libpredict's hook read.
- The macro path collapses to: if not the current target, swap target,
  run the loadstring'd func, restore the previous target.
- 99 lines → 34.

libs/libpredict.lua:
- Drop the dead `local mouseover = pfUI.uf.mouseover.unit` plumbing in
  the CastSpellByName hook — pfUI.uf.mouseover is gone and the field
  was permanently nil anyway. The three `target or mouseover or default`
  fallback chains collapse to `target or default`.

Modern mouseover/click-to-cast detection in libpredict goes through
pfUI.libpredict_pending_cast (populated by libdebuff from Nampower's
SPELL_CAST_EVENT) — that path is GUID-based, server-authoritative, and
untouched.

modules/mouseover.lua

@@ -1,39 +1,6 @@
 pfUI:RegisterModule("mouseover", function ()
-  pfUI.uf.mouseover = CreateFrame("Frame", "pfMouseOver", UIParent)
-
-  -- Prepare a list of units that can be used via SpellTargetUnit
-  local st_units = { [1] = "player", [2] = "target", [3] = "mouseover" }
-  for i=1, MAX_PARTY_MEMBERS do table.insert(st_units, "party"..i) end
-  for i=1, MAX_RAID_MEMBERS do table.insert(st_units, "raid"..i) end
-
-  -- Try to find a valid (friendly) unitstring that can be used for
-  -- SpellTargetUnit(unit) to avoid another target switch
-  local function GetUnitString(unit)
-    for index, unitstr in pairs(st_units) do
-      if UnitIsUnit(unit, unitstr) then
-        return unitstr
-      end
-    end
-
-    return nil
-  end
-
-  -- Same as CastSpellByName but with disabled AutoSelfCast
-  local function NoSelfCast(spell, onself)
-    local cvar_selfcast = GetCVar("AutoSelfCast")
-
-    if cvar_selfcast ~= "0" then
-      SetCVar("AutoSelfCast", "0")
-      pcall(CastSpellByName, spell, onself)
-      SetCVar("AutoSelfCast", cvar_selfcast)
-    else
-      CastSpellByName(spell, onself)
-    end
-  end
-
   _G.SLASH_PFCAST1, _G.SLASH_PFCAST2 = "/pfcast", "/pfmouse"
   function SlashCmdList.PFCAST(msg)
-    local restore_target = true
     local func = pfUI.api.TryMemoizedFuncLoadstringForSpellCasts(msg)
     local unit = "mouseover"
 
@@ -50,51 +17,18 @@ pfUI:RegisterModule("mouseover", function ()
       end
     end
 
-    -- Nampower: CastSpellByName supports a second unit parameter directly.
-    -- unit is already resolved to "mouseover", "target" or "player" at this point.
-    if not func and GetNampowerVersion then
+    -- Spell-name path: Nampower's CastSpellByName takes a second unit
+    -- parameter directly, no target swap dance required.
+    if not func then
       CastSpellByName(msg, unit)
       return
     end
 
-    -- If target and mouseover are friendly units, we can't use spell target as it
-    -- would cast on the target instead of the mouseover. However, if the mouseover
-    -- is friendly and the target is not, we can try to obtain the best unitstring
-    -- for the later SpellTargetUnit() call.
-    local unitstr = not UnitCanAssist("player", "target") and UnitCanAssist("player", unit) and GetUnitString(unit)
-
-    if UnitIsUnit("target", unit) or (not func and unitstr) then
-      -- no target change required, we can either use spell target
-      -- or the unit is already our current target.
-      restore_target = false
-    else
-      -- The spelltarget can't be used here, we need to switch
-      -- and restore the target during spell cast
-      TargetUnit(unit)
-    end
-
-    if func then
-      func()
-    else
-      -- write temporary unit name
-      pfUI.uf.mouseover.unit = unit
-
-      -- cast without self cast cvar setting
-      -- to allow spells to use spelltarget
-      NoSelfCast(msg)
-
-      -- set spell target to unitstring (or selfcast)
-      if SpellIsTargeting() then SpellTargetUnit(unitstr or "player") end
-
-      -- clean up spell target in error case
-      if SpellIsTargeting() then SpellStopTargeting() end
-
-      -- remove temporary mouseover unit
-      pfUI.uf.mouseover.unit = nil
-    end
-
-    if restore_target then
-      TargetLastTarget()
-    end
+    -- Macro path: switch target so the macro's spell calls land on `unit`,
+    -- then restore.
+    local restore_target = not UnitIsUnit("target", unit)
+    if restore_target then TargetUnit(unit) end
+    func()
+    if restore_target then TargetLastTarget() end
   end
 end)