Remove using directives ("using namespace x") from tools/traffic_annotation/.

Bug: 82078
Change-Id: Iaf572972b0285c020621899345f8c1ab7263b2a3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1881781
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Ramin Halavati <rhalavati@chromium.org>
Reviewed-by: Ramin Halavati <rhalavati@chromium.org>
Cr-Commit-Position: refs/heads/master@{#709809}

tools/traffic_annotation/auditor/traffic_annotation_auditor_unittest.cc

@@ -50,8 +50,6 @@ const base::FilePath kClangToolPath =
 const std::set<int> kDummyDeprecatedIDs = {100, 101, 102};
 }  // namespace
 
-using namespace testing;
-
 class TrafficAnnotationAuditorTest : public ::testing::Test {
  public:
   void SetUp() override {