I was looking through Revenge of the Sith's transcript to answer a question, and I found this:
The Jedi QUINLAN VOS is riding on top of a CLONE TURBO TANK. The main cannon of a second tank slowly swings to point right at him and a COUPLE OF CLONES. The cannon fires, and QUINLAN VOS and the CLONES disappear in a huge EXPLOSION.
Looking on Wookieepedia, I found this:
The character, as fleshed out in the Expanded Universe, eventually caught Lucas' eye. The director was intrigued by Vos and decided to include him in the 2005 film Star Wars: Episode III Revenge of the Sith. The character was scripted to appear on the planet Kashyyyk, the Wookiee homeworld, during the execution of Order 66, but the scene was cut before the scene was shot or an actor was cast. An animatic featuring Vos was developed, however, and a passing reference to the character remained in the final film
Have any reasons been given as to why this scene was cut?