Fix talkback ordering of zen duration dialog

zen_mode_condition elements do not have unique ids, so when assigning
the accessibility traversal order in ZenRadioLayout, the hidden
more/less buttons in the ZenRadioLayout were causing an improper
traversal order for the visible more/less buttons. This fix removes the
unused buttons.

Test: manual
Fixes: 145261528
Change-Id: I2750a5484da52723fb363d138b600f87792f6552