multimedia/webcamd: clarify version requirements in consumers

webcamd exposes V4L/DVB/EVDEV/etc devices with consumer ABI configured
by v4l_compat version during build. Drop >0 dummy as V4L is available
since day 1 and we only want the daemon. This syncs RUN_DEPENDS with:

multimedia/gstreamer-plugins-v4l2
multimedia/gstreamer1-plugins-v4l2