Revert "Camera: open Camera and start Preview in a seperate thread."

Start openCamera and start preview in a separate thread so that
UI initialization and preview can run parallely. This is to
improve camera cold start latency.

Change-Id: I57af45bc90a4db1630c73449d543c3ff0992e55c (reverted from commit 9ca415b446d5f79876fd2e3d5847f6191494a92b)