n1500
 

where it says you can remove target ninja from its team and that ninja cant be sent out to battle during this turn.

is removing the target ninja from its team optional? meaning can you still target a ninja without removing it from the team in order to effect that ninjas whole team?

does not affect the Ninja's team.
Optional means you choose whether or not to use the effect. If you chose to use n1500's effect, you would target a Ninja. If you choose not to use the effect, you would not target a Ninja.