Delete more event tracing macros (take 2)

Also tried to clean up the comments to be clearer.

Re-land of: https://skia-review.googlesource.com/25364, with some
macros that are used by Flutter restored.

Change-Id: I648815c275dfea2ec83a382a633af8d9f7780512
Reviewed-on: https://skia-review.googlesource.com/25561
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Brian Osman <brianosman@google.com>
3 files changed