Various debug conditional compilation cleanup (#2915)

* Global: Define DEBUG as 0 if not already defined

* Clean up DEBUG-guarded code

src/d/actor/d_a_npc_grr.cpp

@@ -215,7 +215,7 @@ daNpc_grR_c::~daNpc_grR_c() {
         mAnm_p->stopZelAnime();
     }
 
-    #ifdef DEBUG
+    #if DEBUG
     if (mHIO != NULL) {
         mHIO->removeHIO();
     }