Revert "camera: SoftHDR: Reinhard tonemap and parallel processing"

This reverts commit ff2b54f65cb320779ba031b33a593e743fb84847.
camera: SoftHDR: Use parallel processing

On an idea from Steve Kondik, the RS script now uses
parallel processing via rsForEach, processing every
line of the image in multiple threads.

Change-Id: I552c61e10abf652c50b8511169886bab0986637e