Remove legacy code for box blur.

Change-Id: I2a4ca5d623adcf923981dd27be40dcbf81152954
Reviewed-on: https://skia-review.googlesource.com/48583
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Herb Derby <herb@google.com>
1 file changed