How to disable two-fingers/right-click in touchpad?

Are you comfortable with the command prompt?

You can configure in detail how you want your touchpad to behave using synclient

You can get a list of current settings by doing synclient -l

For your specific request, you will need to run synclient TapButton2=0 to dissable the feature. To make the feature persistent create a ~/touchpad.sh configuration.

More info...

To summarize most everything that everyone has said, just open a console and run the following three commands:

echo "synclient TapButton2=0" > ~/.touchpad.sh
chmod +x ~/.touchpad.sh
gsettings set org.gnome.settings-daemon.peripherals.input-devices hotplug-command “~/.touchpad.sh”