Update torch floor divide ops

Summary: Using `//` for torch floor divide is deprecated (and prints an annoying warning). There were 2 instances of this in replicated.py. This diff removes them.

Reviewed By: yuansen23

Differential Revision: D35188089

fbshipit-source-id: e897a42345ab2292fa66c424106badf441e58f95

crypten/mpc/primitives/replicated.py

@@ -118,10 +118,10 @@ def truncate(x, y):
     rank = x.rank
 
     if rank == 0:
-        x.share //= y
+        x.share = x.share.div(y, rounding_mode="trunc")
     elif rank == 1:
         x2 = comm.get().recv(x.share, 2)
-        x.share = x.share.add(x2) // y
+        x.share = x.share.add(x2).div(y, rounding_mode="trunc")
     elif rank == 2:
         comm.get().send(x.share, 1)
         x.share -= x.share