Remove flag --r_split

[festutz]

With the new annotations framework, we prioritize round robin over the previous standard parallelization (aka consecutive chunks parallelization). In contrast to before, both types of parallelization might be used (for different command invocations). Thus, the flag --r_split is pointless and can be removed.

NOTE: this shall only be addressed once #623 has been merged to future.

[angelhof]

Fixed in #640