Remove use of autopilot simulated keyboard when using OSK

[Richard Huddie]

It is now the case that if Unity8 detects a keyboard it will automatically hide the OSK and stop it from appearing. This includes the simulated keyboard used by Autopilot.

Now that textfield.write() supports using OSK, we should remove all instances of the autopilot simulated keyboard when the OSK is being used. The simulated keyboard is currently used to send Home and End key events to move the cursor to the start or end of a string, because these keys are not present on the OSK.

Some new helper methods in ubuntu_keyboard now allow the Home and End key events to be sent through the maliit-server without having to create a new simulated keyboard, which would cause Unity8 to hide the OSK. So the textfield helper methods should be updated to use the new helpers from ubuntu_keyboard and remove usage of the autopilot simulated keyboard when the OSK is being used.