Remove aconfig flags for Connectivity FlaggedAPI annotations

Split flags.aconfig to platform flags and module flags.
Platform flags are used from platform code.
Module flags are used for FlaggedAPI annotations in modules.

This CL cherry-pick ag/25977118 to aosp-main-future.
After this CL, aosp/2919289 can be merged.

Bug: 321624552
Test: TH
Change-Id: Ie8e0f911d0f7d7e81d108b8e8ab539b29a255ad0
Merged-In: Ie8e0f911d0f7d7e81d108b8e8ab539b29a255ad0