Revert "[sql] Validate database files before enabling memory-mapping."

Revert "[sql] Validate database files before enabling memory-mapping."

This reverts commit de8784cf209f5c254f6c65718373985eb662b36f.

Reason for Revert:
Implicated in test failures:
ChromeMainTest.ReuseBrowserInstanceWhenOpeningFile
ChromeMainTest.SecondLaunch
ChromeMainTest.SecondLaunchFromIncognitoWithNormalUrl
DiagnosticsControllerTest.RecoverFromNssCertDbFailure
DiagnosticsControllerTest.RecoverFromNssKeyDbFailure

First failing bot:
https://build.chromium.org/p/chromium.chromiumos/builders/Linux%20ChromiumOS%20Tests%20%28dbg%29%281%29/builds/8908

Original Issue:
https://codereview.chromium.org/1426743006

TBR=shess@chromium.org, isherman@chromium.org, rmcilroy@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=537742
Committed: https://crrev.com/1736cd0fb260d29ac0df3f05a092b99f7933bf07
Cr-Commit-Position: refs/heads/master@{#358709}

[robliao, 2015-11-10 00:08:57]

The CQ bit was checked by robliao@chromium.org

[commit-bot: I haz the power, 2015-11-10 00:10:33]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1432953002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1432953002/1

[commit-bot: I haz the power, 2015-11-10 00:13:34]

Committed patchset #1 (id:1)

[Scott Hess - ex-Googler, 2015-11-10 00:14:25]

LGTM.  Can't see how this fails there with that error but it doesn't fail in the
statement immediately after the Open(), but evidence is pretty clear...

[commit-bot: I haz the power, 2015-11-10 00:14:57]

Patchset 1 (id:??) landed as
https://crrev.com/1736cd0fb260d29ac0df3f05a092b99f7933bf07
Cr-Commit-Position: refs/heads/master@{#358709}