Remove mapOrphanTransactionsByPrev from DoS_tests

This is another violation of the one definition rule, as the type
for mapOrphanTransactionsByPrev did not match the one in
net_processing.cpp anymore. As it now depends on a custom Iterator,
it seems too much hassle to correctly expose it to the tests.
Instead, this commit just removes the one test it was referenced in.

src/test/DoS_tests.cpp

@@ -32,7 +32,6 @@ struct COrphanTx {
     int64_t nTimeExpire;
 };
 extern std::map<uint256, COrphanTx> mapOrphanTransactions;
-extern std::map<uint256, std::set<uint256> > mapOrphanTransactionsByPrev;
 
 CService ip(uint32_t i)
 {
@@ -203,7 +202,6 @@ BOOST_AUTO_TEST_CASE(DoS_mapOrphans)
     BOOST_CHECK(mapOrphanTransactions.size() <= 10);
     LimitOrphanTxSize(0);
     BOOST_CHECK(mapOrphanTransactions.empty());
-    BOOST_CHECK(mapOrphanTransactionsByPrev.empty());
 }
 
 BOOST_AUTO_TEST_SUITE_END()