src: remove unused variable

This fixes a compiler warning.

PR-URL: #17150
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

src/node.cc

@@ -887,7 +887,6 @@ void SetupDomainUse(const FunctionCallbackInfo<Value>& args) {
   env->set_using_domains(true);
 
   HandleScope scope(env->isolate());
-  Local<Object> process_object = env->process_object();
 
   CHECK(args[0]->IsArray());
   env->set_domains_stack_array(args[0].As<Array>());