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_zelRo.cpp

@@ -251,7 +251,7 @@ int daNpc_ZelRo_c::Draw() {
     }
 
     return draw(
-#ifdef DEBUG
+#if DEBUG
         chkAction(&daNpc_ZelRo_c::test),
 #else
         FALSE,
@@ -626,12 +626,10 @@ int daNpc_ZelRo_c::talk(void* param_1) {
     return 0;
 }
 
-#ifdef DEBUG
 int daNpc_ZelRo_c::test(void* param_1) {
     int rt = 0;
     return rt;
 }
-#endif
 
 static int daNpc_ZelRo_Create(void* a_this) {
     return static_cast<daNpc_ZelRo_c*>(a_this)->create();