tests: Remove now-unnecessary manual Unload's

These manual calls to Unload() are no longer necessary because
CBlockIndex's no longer live in the heap as of the previous commit.

src/test/validation_chainstate_tests.cpp

@@ -72,9 +72,6 @@ BOOST_AUTO_TEST_CASE(validation_chainstate_resize_caches)
         // The view cache should be empty since we had to destruct to downsize.
         BOOST_CHECK(!c1.CoinsTip().HaveCoinInCache(outpoint));
     }
-
-    // Avoid triggering the address sanitizer.
-    WITH_LOCK(::cs_main, manager.Unload());
 }
 
 //! Test UpdateTip behavior for both active and background chainstates.