fix up! Remove thread for preview callback when stop preview

fix up! Remove thread for preview callback when stop preview

- The thread leak is occurred with below sequence and it causes deadlock after some time.
 1. Process A calls camera_start_preview(). -> create thread for preview callback
 2. Process B calls camera_start_preview().
 3. Process A gets interrupted callback and the state of camera handle is changed to CAMERA_STATE_CREATED.
    Then, process A's preview callback thread is remained, because it is released in camera_stop_preview(),
    but, it's skipped by interrupt.

[Version] 0.4.71
[Issue Type] Bug fix

Change-Id: Ifaafb52ed3e549d3a6203754ec6fa90079893cb5
Signed-off-by: Jeongmo Yang <jm80.yang@samsung.com>