merge and merge_sort in subworkflow are not useful

[Cao Fan]

    scatter(i in range(5)){
        call merge { input:
            bam_files = bams_to_merge[i]
        }
    }
  
    call merge_sort { input:
        sort_files_ = fragment.sort_file
    } 

in process_library.wdl are time consuming and not useful. They basically copy the output files of the fragment step as the fragment outputs are all single files as defined by

 output {
        File collisions = glob("collisions.bam")[0]
        File collisions_low_mapq = glob("collisions_low_mapq.bam")[0]
        File unmapped = glob("unmapped.bam")[0]
        File mapq0 = glob("mapq0.bam")[0]
        File alignable = glob("alignable.bam")[0]
        File sort_file = glob("sort.txt")[0]
        File norm_res = glob("result.res.txt")[0]
        File stats_sub_result = glob("alignment_stats.txt")[0]
        File stats_sub_result_json = glob("alignment_stats.json")[0]
}