Get rid of unused class SearchBuffer

This patch gets rid of unused class |SearchBuffer| and related files for
improving code health.

Since the CL[1], nobody use this class.

[1] http://crrev.com/c/1451697: Make FindStringBetweenPositions use FindBuffer
and activate invisible matches

Change-Id: I36589acdc8e00d89f7fc2cc6d028a84e2389ea2f
Reviewed-on: https://chromium-review.googlesource.com/c/1457702
Auto-Submit: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Rakina Zata Amni <rakina@chromium.org>
Reviewed-by: Rakina Zata Amni <rakina@chromium.org>
Cr-Commit-Position: refs/heads/master@{#630103}
5 files changed