Consolidate `gtftogenepred` modules

[atrigila]

There is a local module and an nf-core module. The local module seems to be in use. It would be worth checking if:

1. The nf-core module can be used and provide the same functionality as the local module (perhaps via configs).
2. Remove the module that is not used from the pipeline.

The current UCSC_CUSTOM_GTFTOGENEPRED process in nf-core/rnafusion duplicates functionality provided by the nf-core/UCSC_CUSTOM_GTFTOGENEPRED module, which already includes tests and all the required structure.

To align rnafusion with nf-core best practices, we should replace the local module with the nf-core module in the pipeline.