test: Remove no longer needed MakeChain calls

These calls are no longer needed after edc316020e
from #19098 which started instantiating BasicTestingSetup.m_node.chain

Patch from MarcoFalke <falke.marco@gmail.com> in
https://github.com/bitcoin/bitcoin/pull/19425#discussion_r526701954

Co-authored-by: MarcoFalke <falke.marco@gmail.com>

src/wallet/test/ismine_tests.cpp

@@ -27,8 +27,7 @@ BOOST_AUTO_TEST_CASE(ismine_standard)
     CKey uncompressedKey;
     uncompressedKey.MakeNewKey(false);
     CPubKey uncompressedPubkey = uncompressedKey.GetPubKey();
-    NodeContext node;
-    std::unique_ptr<interfaces::Chain> chain = interfaces::MakeChain(node);
+    std::unique_ptr<interfaces::Chain>& chain = m_node.chain;
 
     CScript scriptPubKey;
     isminetype result;