draw: remove set-but-unused variable

src/gallium/auxiliary/draw/draw_vertex.c

 void
 draw_dump_emitted_vertex(const struct vertex_info *vinfo, const uint8_t *data)
 {
-   unsigned i, j;
+   unsigned i;
 
    for (i = 0; i < vinfo->num_attribs; i++) {
-      j = vinfo->attrib[i].src_index;
       switch (vinfo->attrib[i].emit) {
       case EMIT_OMIT:
          debug_printf("EMIT_OMIT:");