Greatly simplify flags for test binaries.

Since we're now calling the shots of what flags get passed in the
recipes, we can just pass the right ones right away and remove all
the flag renaming.

--isolated-script-test-output is no longer passed, so we can just
remove it. The recipe is currently passing
--isolated-script-perf-test-output but I will start passing the
underscore version shortly.

Bug: chromium:1051927
Change-Id: I571090e62f79ea17c793295df7f5abb21f45d207
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/171681
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Patrik Höglund <phoglund@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30878}

test/test_main_lib.cc

@@ -60,11 +60,6 @@ ABSL_FLAG(
 
 #else
 
-ABSL_FLAG(std::string,
-          isolated_script_test_output,
-          "",
-          "Path to output an empty JSON file which Chromium infra requires.");
-
 ABSL_FLAG(
     std::string,
     isolated_script_test_perf_output,
@@ -190,14 +185,6 @@ class TestMainImpl : public TestMain {
     if (metrics_to_plot) {
       webrtc::test::PrintPlottableResults(*metrics_to_plot);
     }
-
-    std::string result_filename =
-        absl::GetFlag(FLAGS_isolated_script_test_output);
-    if (!result_filename.empty()) {
-      std::ofstream result_file(result_filename);
-      result_file << "{\"version\": 3}";
-      result_file.close();
-    }
 #endif
 
     if (capture_events) {