bitstream: remove dead assignment

Change-Id: I2a4c394e885075a5c16986335feb363c49991916

vp10/encoder/bitstream.c

diff --git a/vp10/encoder/bitstream.c b/vp10/encoder/bitstream.c
index 6db69a1..5bf9f98 100644
--- a/vp10/encoder/bitstream.c
+++ b/vp10/encoder/bitstream.c
@@ -182,7 +182,6 @@
     }
   }
   savings = 0;
-  do_update = 0;
   for (i = TX_4X4; i < EXT_TX_SIZES; ++i) {
     savings += prob_diff_update_savings(
         vp10_ext_tx_tree, cm->fc->inter_ext_tx_prob[i],