Update documentation - No manual IRODS authentication necessary

[KuechlerO]

Is your feature request related to a problem? Please describe.
Hey, just a quick mention:
It seems like the manual IRODS authentication is not necessary anymore.
Hence the iinit step is not required.
It is mentioned here:
https://cubi-tk.readthedocs.io/en/latest/man_ingest_fastq.html

Describe the solution you'd like
Removal of this documentation part.

Additional context
I've used the cubi-tk ingest-fastq from a server without system IRODS installed.
However, it still worked just fine as long as the irods_environment.jsonis placed correctly.