test: remove unused using declarations

PR-URL: #18637
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>

test/cctest/test_environment.cc

@@ -5,12 +5,6 @@
 #include "gtest/gtest.h"
 #include "node_test_fixture.h"
 
-using node::Environment;
-using node::IsolateData;
-using node::CreateIsolateData;
-using node::FreeIsolateData;
-using node::CreateEnvironment;
-using node::FreeEnvironment;
 using node::AtExit;
 using node::RunAtExit;