draw: remove unused 'start' variable in draw_stats_clipper_primitives()

It was computed, but never actually used.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
diff --git a/src/gallium/auxiliary/draw/draw_context.c b/src/gallium/auxiliary/draw/draw_context.c
index da1e958..0a67879 100644
--- a/src/gallium/auxiliary/draw/draw_context.c
+++ b/src/gallium/auxiliary/draw/draw_context.c
@@ -1043,11 +1043,8 @@
                               const struct draw_prim_info *prim_info)
 {
    if (draw->collect_statistics) {
-      unsigned start, i;
-      for (start = i = 0;
-           i < prim_info->primitive_count;
-           start += prim_info->primitive_lengths[i], i++)
-      {
+      unsigned i;
+      for (i = 0; i < prim_info->primitive_count; i++) {
          draw->statistics.c_invocations +=
             u_decomposed_prims_for_vertices(prim_info->prim,
                                             prim_info->primitive_lengths[i]);