Revert "Change the Ambient Context Manager to return...

Revert "Change the Ambient Context Manager to return STATUS_SERVICE_UNAVAILABLE instead of STATUS_NOT_SUPPORTED when the detection service is not set up."

This reverts commit 49938fc3.

Reason for revert: the owner (kxchen@) says their client relies on STATUS_NOT_SUPPORTED to know whether AiAi service is available. And she will change the status code logic with some other improvements.

Change-Id: I64785f224ded5b8f6b3d26f6865d5c1a017ad9d6