Use the correct Smart Storage flag in SettingsLib.

Previously, the show_opt_in and enabled flags were conflated to
basically mean the same thing. Because we are now distinctly making
show_opt_in refer to showing a toggle to opt into the feature in SUW and
enabled to mean the default enabled status, we need to change the
utility method for querying the default enabled status.

Bug: 122461924
Test: RunSettingsLibRoboTests
Change-Id: I9802d307597d90514e7dc6631998daa1d2fab253
Merged-In: I9802d307597d90514e7dc6631998daa1d2fab253