unpack-trees: don't shift conflicts left and right

unpack-trees: don't shift conflicts left and right

If o->merge is set, the struct traverse_info member conflicts is shifted
left in unpack_callback, then passed through traverse_trees_recursive
to unpack_nondirectories, where it is shifted right before use.  Stop
the shifting and just pass the conflict bit mask as is.  Rename the
member to df_conflicts to prove that it isn't used anywhere else.

Signed-off-by: René Scharfe <redacted>
Signed-off-by: Junio C Hamano <redacted>