Make dex2oat(d) and hiddenapi 64-bit only on host.

Following https://r.android.com/1239726 we no longer need multilib host
dex2oat.

Also clean up a prefer32 device override that isn't applicable for the
host-only hiddenapi binary.

Test: m (with and without HOST_PREFER_32_BIT=true)
Test: art/build/apex/runtests.sh (with and without HOST_PREFER_32_BIT=true)
Test: lunch sdk-eng && art/tools/buildbot-build.sh --host && \
  art/test/run-test --host --optimizing 641-checker-arraycopy
  (with and without HOST_PREFER_32_BIT=true)
Bug: 148372405
Bug: 149749169
Change-Id: I46256ad7e8778e8d0f24b40d5acde482c4b66971
4 files changed