sql: Remove references to USE_SYSTEM_SQLITE.

USE_SYSTEM_SQLITE used to be supported on iOS, and now is a no-op.
This CL removes the references to it from //sql, to avoid confusing
readers.

The CL also breaks down an unnecessarily large unit test in
//sql/connection_unittest.cc that happend to be near the changes in this
CL.

Change-Id: I47c324300b54362529364a5ef26ee45b45fe3b76
Reviewed-on: https://chromium-review.googlesource.com/1137921
Reviewed-by: Chris Mumford <cmumford@chromium.org>
Reviewed-by: Daniel Murphy <dmurph@chromium.org>
Commit-Queue: Daniel Murphy <dmurph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576213}
5 files changed