Hi !
I’ve just download Audacity 2.1.0 for my Mac on macOS 10.12.6 and I don’t have access to the Vocal Remover Plug-in on the Effect Menu … I’ve tried to “install” or “add” the plug in vocalremover.ny present in the Audacity Folder but nothing happen … Every plug in present in that folder are not install in Audacity, I just have the Audio Units … 
Thanks a lot for your help, have a nice day ! 
That’s an old version.
The current version is 2.2.0 and is available via the Audacity website: https://www.audacityteam.org/download/mac/
The Vocal Remover effect is installed by default, though I would also suggest that you also try the new “Vocal Reduction and Isolation” effect. You can find out more about the new effect from the manual: http://manual.audacityteam.org/man/vocal_reduction_and_isolation.html
Ensure that you install Audacity according to the instruction on the download page, otherwise many of the included effects will be unavailable.