Remove unnecessary exception from Title::getLatestRevID()

Bug 37209: An exception was thrown where the data cached in the Title
object was inconsistent with the data in LinkCache. It shouldn't be
surprising that this happens, since there is no guarantee that the data
was derived from the same transaction or even the same DB server.

But I don't think it is a problem worth troubling the user over, since
with $flags=0, the slave DB server will be used, and no special guarantee
of consistency should be expected by callers. If callers do need
consistency, then they should make their own arrangements to get it,
such as clearing the LinkCache.

Since we have to pick a winner, and the choice is mostly arbitrary since
it's not possible to tell which is fresher, I think LinkCache is a better
choice since the lifetime of its cache entries can be controlled.

Change-Id: I0add48463341e56fe8c155b1007487278ad2705d
Merge "Remove unnecessary exception from Title::getLatestRevID()"