Revert "Introduce optional sequential_output/2 callback"

[PragTob]

This reverts commit dfa6987a5e1c8db0a6629fad70127097d3bc9577.

It turned out that the parallel processing wasn't the issue with memory consumption we faced but instead copying data to processes.

See:

• 408

• 414

• https://pragtob.wordpress.com/2023/12/18/careful-what-data-you-send-or-how-to-tank-your-performance-with-task-async/