Also disable dexpreopt for boot images for unbundled builds.

This fixes the tradefed build error caused by aosp/2582191.

Bug: 280440941
Test: `BUILD_BROKEN_DISABLE_BAZEL=true m dist` on tradefed branch.
(cherry picked from https://android-review.googlesource.com/q/commit:c74a4011e2815f2ffc3815176c958a0fdabbd621)
Merged-In: I34c9fea0a5f7110c9b2bda1986df82afa3eafc79
Change-Id: I34c9fea0a5f7110c9b2bda1986df82afa3eafc79