Remove 'x' policy for non-default DSDS SIM

This CL changes the policy for showing the 'x' on the mobile signal
indicator such that we do not show an 'x' when a subscription has an
icon group of NOT_DEFAULT_DATA, except in the case where mobile data is
turned off on the default subscription

Test: atest SystemUITests; manual
Fixes: 135457552
Change-Id: Ie21462be12a9920d9b2830039f4095c5bd82bd2c