Add deprecation message for MICRO_AI_GUARDIAN macro

data/core/macros/ai_micro_ais.cfg

@@ -291,6 +291,28 @@
         [/engine]
         {RCA_STAGE}
     [/ai]
+
+    # Somewhat hacky way to get a deprecation message displayed
+    # This macro goes into the [side] tag, so ActionWML tags cannot be used
+    [unit]
+        type=Fog Clearer
+        x,y=1,1
+        id=ai_micro_ai_guardian_fake_unit
+
+        [event]
+            name=prestart
+            id=ai_micro_ai_guardian_deprecation_message
+
+            [wml_message]
+                logger=warn
+                message = "The MICRO_AI_GUARDIAN macro is deprecated.  Use the macros for the individual guardian Micro AI engines instead."
+            [/wml_message]
+
+            [kill]
+                id=ai_micro_ai_guardian_fake_unit
+            [/kill]
+        [/event]
+    [/unit]
 #enddef
 
 #define MICRO_AI_COWARD