Avoid VarHandle checks for boot image field VarHandles. am: 9d31daa0b3 am: f08f2e3895

Original change: https://android-review.googlesource.com/c/platform/art/+/2069110

Change-Id: Ia2f8077e3a364c0fcf7138ba2a642b09cb2320e0
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>