fdr: rely on fixed size confirm structures

src/fdr/fdr_confirm_runtime.h

@@ -101,7 +101,7 @@ void confWithBit(const struct FDRConfirm *fdrc, const struct FDR_Runtime_Args *a
         *control = a->cb(loc - buf, i, li->id, a->ctxt);
     out:
         oldNext = li->next; // oldNext is either 0 or an 'adjust' value
-        li = (const struct LitInfo *)((const u8 *)li + oldNext + li->size);
+        li++;
     } while (oldNext);
 }