Make the boot image always multi-image.

Deprecate the --multi-image option.

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Test: Pixel 2 XL boots.
Test: m test-art-target-gtest
Test: testrunner.py --target --optimizing
Bug: 77856493
Change-Id: I01fd02341cb4dc4fa75a388071694b51ba0bc5f7
4 files changed