ports/156580: audio/vorbis-tools: optionally get rid of libkate dependency

[Barbara]

Note that the patch doesn't remove the dependency if someone doesn't want to!!!
It just add an option yet offered from libkate authors! Just like many other 
ports!
I think that most of the people having vorbis-tools installed don't even know 
what is libkate.

And as I posted a fix for libkate (which is still missing the dependecy from 
python!!!) in pr 155280 about two months ago, and it seems that the maintainer 
is not active since *long* time, can someone please review/comment/commit that 
pr instead of just closing this one?