Clean up SqlSkipPreload feature.

Bug: 1126640
Change-Id: I87de57b6c22c6b2f7bda8c6ca6a8b501436f863b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2435327


Reviewed-by: Victor Costan <pwnall@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Commit-Queue: Caitlin Fischer <caitlinfischer@google.com>
Cr-Commit-Position: refs/heads/master@{#812006}