LiveDisplaySettings: Unlock Reading Mode whenever is possible

Don't hide it anymore if Digital Wellbeing is present as this package
no longer provides the same functionality as before. It has a greyscale
option, but only when bedtime mode is enabled. User might want to enable
Reading Mode independently, so make it available.

This partially reverts commit 1b1932c0.

Change-Id: Icacd81362d3cf83ced67ff07aed41ffb44af35ec