Properly define v8_enable_inspector and its override in GN.

test/inspector/BUILD.gn

 # Copyright 2016 the V8 project authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("../../gni/v8.gni")
-import("//build_overrides/v8.gni")
 
-if (v8_enable_inspector_override) {
+if (v8_enable_inspector) {
   v8_executable("inspector-test") {
     testonly = true
 
     sources = [
       "inspector-impl.cc",
       "inspector-impl.h",
       "inspector-test.cc",
       "task-runner.cc",
       "task-runner.h",
     ]
 
     configs = [
       "../..:external_config",
       "../..:internal_config_base",
     ]
 
     deps = [
       "../..:v8",
       "../..:v8_libbase",
       "../..:v8_libplatform",
       "//build/config/sanitizers:deps",
       "//build/win:default_exe_manifest",
     ]
 
     cflags = []
     ldflags = []
   }
 }