Jit: fix for 2483131 - VM daemon thread shutdown with JIT enabled

As part of shutdown, the Jit needs to unchain all translations so that
they can respond to suspend requests.  This change introduces a
dvmJitUnchainAll() into shutdown, and also removes some previous
housecleaning that freed our key tables.  We can't actually free those
because suspended threads in the process of shutting down may hold
references.

Change-Id: I7aad332e7195a94970c25a25b2d9fda5607bec08