It's not a "proper" abbreviation in the sense of "commonly used". I don't think there is one for *vorheriger*. Same is true for *Install.* as an abbreviation for *Installation*.

I see how these came to be. The German translation is obviously much longer than the English text, there probably wasn't enough space on the UI, so they made up abbreviations that were as unambiguous as possible while just fitting the space. I have done similar things. 

As Janka states in a comment, *voriger* would have been a good/better alternative (if the *previous* installation is what is meant). The abbreviation *vorh.* is ambiguous, I would normally understand it to mean *vorhanden*.