test, bench: remove globals vCoins and testWallet from test and bench

adapted from a5595b1 and 5e54aa9 in bitcoin#23288. changes to
coinselector_tests must be reverted before backports related to it
are done as these changes are primarily motivated by bitcoin#21866
taking away the global chainstate, which breaks coinselector_tests and
these changes skips over a lot of backporting, making them incompatible
with backporting efforts (or even the commits its adapted from).

the existing behaviour was that it creates its own testNode but doesn't
populate it with a ChainstateManager (or much at all) while the rest of
the client uses WalletTestingSetup's values. for the longest time this
was fine because addCoins > listMNCollaterials > ChainActive() meant that
it was using the fallback, but when chainstate globals are removed,
WalletTestingSetup's values can't serve as a fallback anymore as it'd
now be looking for NodeContext::chainman::m_chain, and chainman wasn't
setup with testNode and the tests crash.

src/bench/coin_selection.cpp

@@ -61,21 +61,16 @@ static void CoinSelection(benchmark::Bench& bench)
 }
 
 typedef std::set<CInputCoin> CoinSet;
-static NodeContext testNode;
-static auto testChain = interfaces::MakeChain(testNode);
-static CWallet testWallet(testChain.get(), /*coinjoin_loader=*/ nullptr, "", CreateDummyWalletDatabase());
-std::vector<std::unique_ptr<CWalletTx>> wtxn;
 
 // Copied from src/wallet/test/coinselector_tests.cpp
 static void add_coin(const CAmount& nValue, int nInput, std::vector<OutputGroup>& set)
 {
     CMutableTransaction tx;
     tx.vout.resize(nInput + 1);
     tx.vout[nInput].nValue = nValue;
-    std::unique_ptr<CWalletTx> wtx = std::make_unique<CWalletTx>(&testWallet, MakeTransactionRef(std::move(tx)));
+    CInputCoin coin(MakeTransactionRef(tx), nInput);
     set.emplace_back();
-    set.back().Insert(COutput(wtx.get(), nInput, 0, true, true, true).GetInputCoin(), 0, true, 0, 0, false);
-    wtxn.emplace_back(std::move(wtx));
+    set.back().Insert(coin, 0, true, 0, 0, false);
 }
 // Copied from src/wallet/test/coinselector_tests.cpp
 static CAmount make_hard_case(int utxos, std::vector<OutputGroup>& utxo_pool)
@@ -93,7 +88,6 @@ static CAmount make_hard_case(int utxos, std::vector<OutputGroup>& utxo_pool)
 static void BnBExhaustion(benchmark::Bench& bench)
 {
     // Setup
-    testWallet.SetupLegacyScriptPubKeyMan();
     std::vector<OutputGroup> utxo_pool;
     CoinSet selection;
     CAmount value_ret = 0;