Revert "dbus_rest: return error response with not found when bad dbus request"

This reverts commit b623d9c1.

Fixes #206

There are conditions where the mapper apparently replies with errors.
While this is obviously wrong, it causes a user facing regression in
firmware updates, which is documented in #206.  This change is likely
just fine in isolation, but someone will need to resolve the mapper
issue before we can re-merge this.

Signed-off-by: Ed Tanous <edtanous@google.com>
Change-Id: I59843b6cc001a81e68b4f82da922b7eb2611ca29