Revert of [Autofill] Merge the autofill_dates table into the autofill table. (https://codereview.chromium.org/166313002/)

Reason for revert:
Broke the GeneralMixMemoryTest.* target from the performance_ui_tests suite.

BUG=347340

Original issue's description:
> [Autofill] Merge the autofill_dates table into the autofill table.
> 
> We already only store two timestamps per autocomplete entry: creation and last
> use.  However, we used to store an arbitrary number of timestamps, and the table
> structure was designed to support that.  Now that that's no longer the case, we
> can dramatically simplify the code.
> 
> The one cost to only keeping two timestamps, rather than all of them, is that
> it's no longer possible to perfectly undo changes in response to a user clearing
> Autofill data for e.g. the last week.  In practice, users are more likely to
> care about having less data stored on disk and traversing the Sync pipes than
> about having perfect frequency information after partially clearing the Autofill
> data.
> 
> BUG=118696
> TEST=unit_tests
> R=estade@chromium.org
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=253380

TBR=estade@chromium.org,pkasting@chromium.org,phajdan.jr@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=118696

Review URL: https://codereview.chromium.org/184183002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254059 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254059