Improve symbols test

Remove seed argument and check for disallowed undefined symbols

Internal.h

@@ -448,6 +448,8 @@ inline std::string printable(const Key &key) {
   return printable(std::string_view((const char *)key.p, key.len));
 }
 
+namespace {
+
 template <class ConflictSetImpl> struct TestDriver {
   // TODO call setOldestVersion, and check range writes/reads
   Arbitrary arbitrary;
@@ -538,5 +540,6 @@ template <class ConflictSetImpl> struct TestDriver {
     return false;
   }
 };
+} // namespace
 
 // GCOVR_EXCL_STOP