src: delete MicroTaskPolicy namespace

PR-URL: #32853
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Michael Dawson <[email protected]>
Reviewed-By: Ruben Bridgewater <[email protected]>
Reviewed-By: Franziska Hinkelmann <[email protected]>

src/api/environment.cc

@@ -23,7 +23,6 @@ using v8::HandleScope;
 using v8::Isolate;
 using v8::Local;
 using v8::MaybeLocal;
-using v8::MicrotasksPolicy;
 using v8::Null;
 using v8::Object;
 using v8::ObjectTemplate;