You can remove target shapes from a blend shape deformer in different ways. With either method, the target shape is removed from the Blend Shape deformer's node, which you can see in the Shape Editor and the Channel Box. The shape animation is re-interpolated for the blend shape to account for this change.
To remove target shapes in the Shape Editor
If you have created target shapes from multiple target objects (see Create blend shapes using multiple target objects), the target shape's corresponding target object is not deleted.
To remove target shapes using Options
The target shape is removed, but not its corresponding target object.