Upgrade deprecated Lua

loadstring was removed, load does the same thing.
atan2 was remvoed, atan works instead

data/ai/lua/ai_helper.lua

@@ -544,7 +544,7 @@ function ai_helper.get_angle(from_hex, to_hex)
     local _, y1cart =  ai_helper.cartesian_coords(x1, y1)
     local _, y2cart =  ai_helper.cartesian_coords(x2, y2)
 
-    return math.atan2(y2cart - y1cart, x2 - x1)
+    return math.atan(y2cart - y1cart, x2 - x1)
 end
 
 function ai_helper.get_direction_index(from_hex, to_hex, n, center_on_east)

data/ai/micro_ais/cas/ca_fast_attack_utils.lua

@@ -90,7 +90,7 @@ local function get_attack_filter_from_aspect(aspect, which, data, is_leader)
         end
     elseif (aspect.name == "lua_aspect") then
         --print("Found lua aspect")
-        local filter = loadstring(aspect.code)(nil, H.get_child(aspect, 'args'), data)
+        local filter = load(aspect.code)(nil, H.get_child(aspect, 'args'), data)
         if (type(filter[which]) == 'function') then
             temporary_attacks_filter_fcn = filter[which]
             local units = AH.get_live_units(attack_filter(which, {

data/lua/wml/random_placement.lua

@@ -14,7 +14,7 @@ wesnoth.wml_actions.random_placement = function(cfg)
 	local math_abs = math.abs	
 	local locs = wesnoth.get_locations(filter)
 	if type(num_items) == "string" then		
-		num_items = math.floor(loadstring("local size = " .. #locs .. "; return " .. num_items)())
+		num_items = math.floor(load("local size = " .. #locs .. "; return " .. num_items)())
 		print("num_items=" .. num_items .. ", #locs=" .. #locs)
 	end
 	local size = #locs