set-verity-state: Refactor & remove even more dead code

Remove even more VB1.0 handling dead code.
Log to both logd and stderr.
Print all debug messages to LOG.
Move all non-externals to annonymous namespace.

Bug: 241688845
Test: adb shell set-verity-state [0|1]
Change-Id: Icda795f185f7bc97607b48d0b529ee02a4580b70