Remove unused renderTask ID span parameter to pre- and post-Flush callbacks

I don't know if we ever actually used this feature. Removing it removes
and needless loop over all the render tasks.

Change-Id: Ife8014c45a34fdec743227dea09e440e0d1d9ea3
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/537516
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
11 files changed