wallet: rename UnloadWallet to WaitForDeleteWallet

And update function's documentation.

src/wallet/test/util.cpp

@@ -74,7 +74,7 @@ void TestUnloadWallet(std::shared_ptr<CWallet>&& wallet)
     // Calls SyncWithValidationInterfaceQueue
     wallet->chain().waitForNotificationsIfTipChanged({});
     wallet->m_chain_notifications_handler.reset();
-    UnloadWallet(std::move(wallet));
+    WaitForDeleteWallet(std::move(wallet));
 }
 
 std::unique_ptr<WalletDatabase> DuplicateMockDatabase(WalletDatabase& database)

src/wallet/test/wallet_tests.cpp

@@ -889,7 +889,7 @@ BOOST_FIXTURE_TEST_CASE(CreateWalletWithoutChain, BasicTestingSetup)
     context.args = &m_args;
     auto wallet = TestLoadWallet(context);
     BOOST_CHECK(wallet);
-    UnloadWallet(std::move(wallet));
+    WaitForDeleteWallet(std::move(wallet));
 }
 
 BOOST_FIXTURE_TEST_CASE(RemoveTxs, TestChain100Setup)