Remove the "UNDONE: ..." printing

Insert an assert instead about what we expect and handle GCInfo-wise.

src/coreclr/jit/emitxarch.cpp

@@ -13128,21 +13128,16 @@ BYTE* emitter::emitOutputIV(BYTE* dst, instrDesc* id)
                     emitRecordRelocation((void*)(dst - sizeof(INT32)), (void*)(size_t)val, IMAGE_REL_BASED_HIGHLOW);
                 }
             }
-
-            // Did we push a GC ref value?
-            if (id->idGCref())
-            {
-#ifdef DEBUG
-                printf("UNDONE: record GCref push [cns]\n");
-#endif
-            }
-
             break;
 
         default:
             assert(!"unexpected instruction");
     }
 
+    // GC tracking for "push"es is done by "emitStackPush", for all other instructions
+    // that can reach here we do not expect (and do not handle) GC refs.
+    assert((ins == INS_push) || !id->idGCref());
+
     return dst;
 }