Drop dead GUID-label branch in unit frame OnEnter

No unit frame ever has a GUID label -- CreateUnitFrame is only ever called
with fixed type names (Player/Target/Focus/Party/Raid/...), and .label is only
ever assigned those. The string.find(this.label, "^0x") branch was a leftover
from an older focus implementation; focus now uses the real "focus" unit
token, so OnEnter always resolves the mouseover via the normal unitstr path.

api/unitframes.lua

@@ -1182,15 +1182,9 @@ end
 function pfUI.uf.OnEnter()
   if not this.label then return end
 
-  -- Nampower: Set native mouseover unit for macro/addon compatibility
-  if SetMouseoverUnit then
-    local unitstr = this.label .. this.id
-    -- For GUID-based frames (focus), use the GUID directly
-    if this.label and string.find(this.label, "^0x") then
-      SetMouseoverUnit(this.label)
-    elseif UnitExists(unitstr) then
-      SetMouseoverUnit(unitstr)
-    end
+  local unitstr = this.label .. this.id
+  if UnitExists(unitstr) then
+    SetMouseoverUnit(unitstr)
   end
 
   if this.config.showtooltip == "0" then return end
@@ -1200,10 +1194,7 @@ function pfUI.uf.OnEnter()
 end
 
 function pfUI.uf.OnLeave()
-  -- Nampower: Clear native mouseover unit
-  if SetMouseoverUnit then
-    SetMouseoverUnit()
-  end
+  SetMouseoverUnit("")
 
   GameTooltip:FadeOut()
 end