Improve symbols test

Remove seed argument and check for disallowed undefined symbols

conflict_set_cxx_api_test.cpp

@@ -3,7 +3,7 @@
 #include <cassert>
 
 int main(void) {
-  ConflictSet cs(0, 0);
+  ConflictSet cs(0);
   ConflictSet::WriteRange w;
   w.begin.p = (const uint8_t *)"0000";
   w.begin.len = 4;