From: Hugh Dickins <hugh@veritas.com>

Jonah Sherman <jsherman@stuy.edu> pointed out back in February how
LO_FLAGS_BH_REMAP is never actually set, since loop_init_xfer only calls
the init for non-0 encryption type.  Fix that or scrap it?  Let's scrap it
for now, that path (hacking values in bio instead of copying data) seems
never to have been tested, and adds to the number of paths through loop:
leave that optimization to some other occasion.