The announcement was that the Hangouts API will no longer be supported. The API was intended for third parties to develop apps that used Hangouts for complementary functions. For example, a maker of video conference systems would use that API to control Hangouts integrated into their product. A provider of CRM (Customer Relationship Management) software would use that API to integrate calling into their contact management system.
The announcement has nothing at all to do with Google Voice. Google Voice uses Hangouts for VoIP calling, which is not using that API, and the VoIP calling function is not going away. It's always possible that Google may shuffle around functions between products, but the important point is that the VoIP calling function isn't being eliminated.