It's still there, just deep in a menu somwhere. Although you don't find dedicated portamento buttons on the panel these days unless you buy something like a Moog "Little Phatty" for example, the function will be under a menu in the voice editing parameters.
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GEAR: Yamaha MOXF-6, Casio MZX-500, Roland Juno-Di, M-Audio Venom, Roland RS-70, Yamaha PSR S700, M-Audio Axiom Pro-61 (Midi Controller). SOFTWARE: Mixcraft-7, PowerTracks Pro Audio 2013, Beat Thang Virtual, Dimension Le.