[Traffic Annotations] Disable clang_tool on waterfall

Now that the "python_script" backend is stable, there's no huge
incentive to keep maintaining the "clang_tool"
backend. win-annotator-rel started getting compilation errors with
clang_tool recently [1], so we might as well disable it.

At the same time, this will make the waterfall bot run much faster,
which should reduce the rate of task timeouts on Windows.

[1] https://ci.chromium.org/p/chromium/builders/ci/win-annotator-rel/1917

Bug: 909867
Change-Id: Ib52cac4a32a41fe11da13fbee2ce85a2b1947c0a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1881307
Commit-Queue: Ramin Halavati <rhalavati@chromium.org>
Reviewed-by: Ramin Halavati <rhalavati@chromium.org>
Auto-Submit: Nicolas Ouellet-Payeur <nicolaso@chromium.org>
Cr-Commit-Position: refs/heads/master@{#709820}

tools/traffic_annotation/scripts/traffic_annotation_auditor_tests.py

@@ -54,30 +54,23 @@ class TrafficAnnotationTestsChecker():
     """
 
     configs = [
-      [                         # Similar to trybot.
+        # Similar to trybot.
+      [
           "--test-only",
           "--error-resilient",
           "--extractor-backend=python_script",
       ],
-      [                         # Failing on any runtime error.
+      # Failing on any runtime error.
+      [
           "--test-only",
           "--extractor-backend=python_script",
       ],
-      [                                      # No heuristic filtering.
+      # No heuristic filtering.
+      [
           "--test-only",
           "--no-filtering",
           "--extractor-backend=python_script",
       ],
-
-      [                         # Clang tool backend.
-          "--test-only",
-          "--extractor-backend=clang_tool",
-      ],
-      [                         # Clang tool backend, no heuristic filtering.
-          "--test-only",
-          "--no-filtering",
-          "--extractor-backend=clang_tool",
-      ],
     ]
 
     self.last_result = None