Remove the separate filer_gtf module that filters for Ensembl_canonical flag

[kkuret]

Is your feature request related to a problem? Please describe

A change in longest_transcript module renders FILTER_GTF module obsolete.

Describe the solution you'd like

Remove the FILTER_GTF module from the pipeline and have everything handled by FIND_LONGEST_TRANSCRIPT module.

Describe alternatives you've considered

Additional context