I have some old sonar project file with several V-vocal clip.These clips can't be played by CbB any more.but how to remove  the v-vocal?

RX 7 has a vocal remover.

Which version of Sonar? If it's a version with region effects, right click and delete the effect. By the way, if you leave the Sonar installation with VVocal in place, doesn't CbB allow using it (as the final version of Sonar did)?

You could perform a minimal install of X2 Producer or older to get V-Vocal back. After selecting the X2 advanced install option, here is what is needed

Once installed, the project will open normally and it is possible to continue using V-Vocal or remove the effect from the clip(s) using Region FX menu.
 
Otherwise, stepping through the plug-ins in safe mode will give an option to skip loading V-Vocal. To open in safe mode hold down the SHIFT key when opening the project.

Isn't V-Vocal the first rendition of a Region FX? I assumed the original audio clip would be in the audio folder (and could re-import it). I also thought saving as a bun and reopening that stripped off V-Vocal information, but not sure how this process behaves with a missing FX.

V-Vocal predates Region FX. It was incorporated into the feature when it was introduced in X3 to look and feel like the ARA-based Region FX. Unlike Audiosnap data, it appears V-Vocal clips may be bundled. Not using either V-Vocal or bundles in years, I just created a project with a V-Vocal clip and bundled it. It open OK with the clip still loaded in V-Vocal.

mettelus I assumed the original audio clip would be in the audio folder...

 
You are correct. That's why you can undo a V-Vocal conversion with CTL-Z. In fact, if you delete the V-Vocal clip you'll find the original file underneath it. All you have to do is un-mute it.