Reland "sql: Remove SQLTestBase."

This is a reland of 525b30a

This reland removes the call to GetDBOptions() from the DatabaseTest
constructor, which was flagged as undefined behavior by the ubsan-vptr
bot. sql::Database construction is deferred to the SetUp() method by
turning the test's sql::Database member into a
std::unique_ptr<sql::Database>.

Original change's description:
> sql: Remove SQLTestBase.
>
> Change-Id: I87bf9499ef590b006660d3b8ab305b0192ec405c
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2866306
> Auto-Submit: Victor Costan <pwnall@chromium.org>
> Commit-Queue: Ayu Ishii <ayui@chromium.org>
> Reviewed-by: Ayu Ishii <ayui@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#879443}

Change-Id: Ie83bf28eaebb88883b9eb37a7d8407e8bfc619ad
Cq-Do-Not-Cancel-Tryjobs: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2878638
Reviewed-by: Ayu Ishii <ayui@chromium.org>
Commit-Queue: Victor Costan <pwnall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#880595}

sql/BUILD.gn

@@ -121,8 +121,6 @@ test("sql_unittests") {
     "test/paths.cc",
     "test/paths.h",
     "test/run_all_unittests.cc",
-    "test/sql_test_base.cc",
-    "test/sql_test_base.h",
     "test/sql_test_suite.cc",
     "test/sql_test_suite.h",
     "transaction_unittest.cc",