[Fixed Bug] Fixed delete[] to free()

[Fixed Bug] Fixed delete[] to free()

[cause]
In mv_engine_config_set_string_attribute(), new[] operator had been changed to malloc()
Thus, the parts calling mv_engine_config_get_string_attribute should have to use free()
instead of delete[] operator.

[solve]
The parts using mv_engine_config_get_string_attribute() is changed to deallocate memory by free()

Change-Id: I60ef4823e43229214c31d0706e53d3aa51c8d600
Signed-off-by: Tae-Young Chung <ty83.chung@samsung.com>