[Traffic Annotation] Update t_a_extractor build instructions

Chrome now supports fuchsia, but t_a_extractor.exe does not. So when
compiling it, we need the `--without-fuchsia` flag.

Change-Id: I04648ae7aaeeb550d3ba4585f7b61bb2423ada3f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1815912
Auto-Submit: Nicolas Ouellet-Payeur <nicolaso@chromium.org>
Commit-Queue: Martin Šrámek <msramek@chromium.org>
Reviewed-by: Martin Šrámek <msramek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#698993}

tools/traffic_annotation/bin/README.md

@@ -10,7 +10,7 @@ in this folder, otherwise run:
 ```bash
 git new-branch roll_traffic_annotation_tools
 python tools/clang/scripts/build.py --bootstrap \
-    --without-android --extra-tools traffic_annotation_extractor
+    --without-android --without-fuchsia --extra-tools traffic_annotation_extractor
 cp third_party/llvm-build/Release+Asserts/bin/traffic_annotation_extractor \
     tools/traffic_annotation/bin/linux64/