[12658] Revert [12653] and use a better fix.

More infos on https://github.com/cmangos/mangos-wotlk/commit/3486cba310f9a301e2ec8e4f9824ed84447f6b76
Sending spline speed instead of complete movement info seem enough no matter if the unit is Player or Creature.
Big thanks to @SilverIce