Use a single library for interacting with vdm flags

Before this CL, there were 3 different libraries for interacting with
vdm aconfig flags, which caused memory leaks in some circumstances.

To simplify the code and avoid confusion, switch to using a single
library instead. Unfortunately, that also means that we need to put that
library into test mode, but currently there isn't a better alternative
available for tests.

Bug: 352596575
Flag: EXEMPT bugfix
Test: m checkinput
Change-Id: Iece976186f1408b8cd5dbaccf4e82dfcb0417ebe