adb: Allow disabling verity on eng builds when using AVB.

Unlike VB1.0, if a device is using AVB then dm-verity is used on any
build (userdebug, eng, etc.). Therefore, we should allow disabling
verity on any build (except USER), not just userdebug. This bug was
pointed out in https://android-review.googlesource.com/#/c/371372/

Bug: 34124301
Test: Manually tested on -eng build on device using AVB.
Change-Id: I314550c13d7458d5d1ef68eb06f98849e11fbe15