Quiet warning by removing unused variable.

fwd_boost_score was not being computed or
referenced, so remove declaration.

Change-Id: Iece36cde1ec113e3c6afaff1407d24cdf12bd0a8
diff --git a/vp8/encoder/firstpass.c b/vp8/encoder/firstpass.c
index 9cdc1e5..8559142 100644
--- a/vp8/encoder/firstpass.c
+++ b/vp8/encoder/firstpass.c
@@ -1473,7 +1473,6 @@
 
     int i;
     double boost_score = 0.0;
-    double fwd_boost_score = 0.0;
     double mv_ratio_accumulator = 0.0;
     double decay_accumulator = 1.0;
     double this_frame_mv_in_out = 0.0;