I've stuck to only doing this in the places where I'm sure we should never get false back. Other places I'm less sure of (and I found more bugs along the way).
This reverts commit 9b52af62b6f469771f2355a964b35ecffa5117d9.
We shouldn't assume that a string maps directly to a legacy ID,
because we might want string aliases (e.g. dark_oak_boat) which refer to
items that have a specific meta value in the MCPE system.
Overall, I want to get rid of the reliance on IDs here and register all
this stuff using closure callbacks on VanillaItems, so getting rid of
this assumption also serves that goal.
