Remove the deprecated sparse_histogram.h header.
Remove the deprecated sparse_histogram.h header.

The functionality provided by this header has been replaced by
equivalent functionality in histogram_functions.h.

R=f1b5a91d4d6ad523f2610114591c007e75d15084@chromium.org

Bug: chromium:773850
Change-Id: I543d5c4d4ab874aaddcf3d9dddf6e486c310cdb0
Reviewed-on: https://chromium-review.googlesource.com/830135
Reviewed-by: Mark Mentovai <f1b5a91d4d6ad523f2610114591c007e75d15084@chromium.org>

chromium/mini_chromium,chromium/mini_chromium,chromium/mini_chromium