Show the target LoS indicator through ClassicAPI's UnitInLineOfSight

The indicator moves from the unitxp module to the target frame, so it no
longer needs UnitXP_SP3. Its checkbox and the shared font size move to a
Target Indicators header; unitxp_font_size becomes indicator_font_size.
The unused pfUI.api.UnitInLineOfSight wrapper, which shadowed the
ClassicAPI global inside the pfUI environment, is removed.

api/api.lua

@@ -59,20 +59,6 @@ function pfUI.api.GetUnitDistance(unit1, unit2)
   return nil
 end
 
--- [ UnitInLineOfSight ]
--- Returns true if unit1 has line of sight to unit2
--- Requires UnitXP_SP3
-function pfUI.api.UnitInLineOfSight(unit1, unit2)
-  if not pfUI.api.HasUnitXP() then return nil end
-  if not unit2 then
-    unit2 = unit1
-    unit1 = "player"
-  end
-  local success, inSight = pcall(UnitXP, "inSight", unit1, unit2)
-  if success then return inSight end
-  return nil
-end
-
 -- [ UnitIsBehind ]
 -- Returns true if unit1 is behind unit2
 -- Requires UnitXP_SP3