Convert isSafetyCenterEnabled from a state flow to a function

Currently, isSafetyCenterEnabled is a state flow that actually never
starts in the product code. As a result, this boolean attribute is
always false as its inital value, even if a physical device can in fact
support safety center. This bug is exposed by the CTS test in the
attached Buganizer issue.

This CL turns the original state flow into a suspend function.

Bug:412769234
Flag:EXEMPT bugfix
Change-Id: I30f89fbf5a231e5d6fa74ef5e8aef54b86bfa88e