src: delete MicroTaskPolicy namespace

PR-URL: #32853
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>

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;