Add deprecation message for <protect_my_unit>

This redundant [goal] can be achieved
with "name=protect_unit" and a side
attribute in the SUF.

changelog

@@ -55,6 +55,7 @@ Version 1.11.4+dev:
      protect_leader=, protect_leader_radius=
    * Fixed bug #20836: advancing units can fire events in [harm_unit] if fire_event=yes
    * Advancing units can be animated by [harm_unit] if animate=yes
+   * Added deprecation message to aspect [goal] when using "name=protect_my_unit".
  * Miscellaneous and bug fixes
    * Fixed minor issue with Drake Clasher animations
    * Added a new playlist FULL_MUSIC_PLAYLIST, which contains all Wesnoth tracks

src/ai/composite/goal.cpp

@@ -18,6 +18,7 @@
  */
 
 #include "goal.hpp"
+#include "wml_exception.hpp"
 #include "../lua/core.hpp"
 #include "../manager.hpp"
 #include "../../log.hpp"
@@ -295,6 +296,9 @@ protect_goal::protect_goal(readonly_context &context, const config &cfg, bool pr
 	, radius_(20) //this default radius is taken from old code
 	, value_(1.0) //this default value taken from old code
 {
+	if(protect_only_own_unit_) {
+		lg::wml_error << deprecate_wml_key_warning("protect_my_unit", "1.13.0") << "\n";
+	}
 }
 
 lua_goal::lua_goal(readonly_context &context, const config &cfg)