emphasize deprecation [documentation tweak]

[MichaelChirico]

Was poking around documentation for formals of this method as I'd seen it recommended and completely missed the Deprecated tag; even after seeing elsewhere it's deprecated, I stared at the documentation for far too long before noticing the existing tag.

So, adding this to emphasize further

[AmplabJenkins]

Can one of the admins verify this patch?

[HyukjinKwon]

I think there are many same instances. We should fix them everywhere consistently. But I don't think it's worth enough fixing everywhere. It's marked as deprecated and so it's deprecated, isn't it?

[MichaelChirico]

@HyukjinKwon this is about usability/user-friendliness. As mentioned, despite being a seasoned R user & increasingly familiar with SparkR documentation, I spent several minutes googling about before realizing the existing "marking".

Happy to try and help file this patch somewhere else if you see fit; just filed here because it's a very easy fix & could be done in-browser without cloning locally/etc

[HyukjinKwon]

If this is the only one, we could try to think differently but I guess there are multiple APIs documented like this. They are all consistently marked in the documentation and in the cod in this way. Unless there's a strong reason to change this kind of convention, I wouldn't fix those.