Undisable the vertex hash backoff

Well, my previous change just broke it which is why it fixed it for me.  numFrames was never being incremented.

I tried a few different things, and it ended up that vertices with < 100 frames are just more likely to abruptly change in some games (mostly ui or sprite sheets.)  Since I had a bunch with hundreds and thousands, I'm hoping those are the ones that are better to cache, anyway?

But maybe I should use `dec.GetDecVtxFmt().stride` instead, or a combination thereof...

Anyway, this fixes it without the glitches while retaining 80% of the performance improvement, so it's at least better than current.  I think it could be improved more.

-[Unknown]