[semantic-sil] Update OME for having mark_uninitialized on the alloc_box instead of project_box.
This consists of just removing support from OME for ensuring that all uses of a
box go through the project_box that has as its user a mark_uninitialized. Since
the lowering of mark_uninitialized onto the relevant project_box is done by
MarkUninitializedFixup pass, I can just rip out the hacks from the OME!
rdar://31521023