swr: remove unnecessary assignment.

I don't see dst_incr/dst_incr_frac ever being changed from their
initial value (which is the inverse of this operation), so it seems
to me that this is a no-op.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libswresample/resample_template.c

@@ -248,7 +248,6 @@ int RENAME(swri_resample)(ResampleContext *c, DELEM *dst, const DELEM *src, int
     if(update_ctx){
         c->frac= frac;
         c->index= index;
-        c->dst_incr= dst_incr_frac + c->src_incr*dst_incr;
     }
 
     return dst_index;