Reduce console noise coming from unit tests:

A few unit tests have historically generated a lot of noise
to the console from log writes.  This noise was not useful
and made it harder to locate actual test failures.

By changing the log level of these tests from
- severities::kError to
- severities::kDisabled
it was possible to remove that noise coming from the logs.

src/test/app/NFTokenDir_test.cpp

@@ -388,7 +388,12 @@ class NFTokenDir_test : public beast::unit_test::suite
         auto exerciseFixNFTokenDirV1 =
             [this,
              &features](std::initializer_list<std::string_view const> seeds) {
-                Env env{*this, features};
+                Env env{
+                    *this,
+                    envconfig(),
+                    features,
+                    nullptr,
+                    beast::severities::kDisabled};
 
                 // Eventually all of the NFTokens will be owned by buyer.
                 Account const buyer{"buyer"};