ART: Reinstate secondary-image-patching exit

Do not attempt imageless running with a stale secondary image. Instead
prune the cache and exit, relying on init restarting the process.

The combined image checksum is not written down into the boot image
itself, only into apps. This should really be fixed.

Follow-up to commit a463b6a9.

(cherry picked from commit 8d8a005a)

Bug: 30832951
Bug: 69428309
Bug: 70213235
Bug: 70498154
Test: m test-art-host
Merged-In: I27ab3384ce4ffd93efb00a2e216cb839fe4357d5
Change-Id: I27ab3384ce4ffd93efb00a2e216cb839fe4357d5