test: remove unused variable in addon test

This fixes the compiler warning for the unused variable in the
report-api addon test.

PR-URL: #44809
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Daeyeon Jeong <daeyeon.dev@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: joyeecheung

test/addons/report-api/binding.cc

@@ -35,8 +35,6 @@ void TriggerReportEnv(const FunctionCallbackInfo<Value>& args) {
 }
 
 void TriggerReportNoEnv(const FunctionCallbackInfo<Value>& args) {
-  Isolate* isolate = args.GetIsolate();
-
   node::TriggerNodeReport(static_cast<node::Environment*>(nullptr),
                           "FooMessage",
                           "BarTrigger",