history: removes README

The refactoring is done, and the structure used is that of other
components, so it's not really interesting to document it here.

BUG=none
TEST=none

Change-Id: I50815cbe3a009b538a35201d673971e8fab3ad86
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2161867
Auto-Submit: Scott Violet <sky@chromium.org>
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#761855}