Have you tried to "clear defaults" or "disable" the voice dialer? Look for it in your Settings / Applications / All. Check if there is a "clear defaults" option.
Most probably there won't be, because installing H2S should already have cleared the defaults for its category of apps. So this leaves the "Disable" option, if there is...
If this works, please let me know, I would like to include the Voice Dialer for CM12 too, so it could be disabled with a single button press, the way I made it for Samsung and LG phones with their default dialers.