Revert "Restore default igenomes behaviour for testing"

This reverts commit 7b063e3.

Author: pinin4fjords

conf/test.config

@@ -24,7 +24,6 @@ params {
     input = "https://raw.githubusercontent.com/nf-core/test-datasets/rnaseq/samplesheet/v3.10/samplesheet_test.csv"
 
     // Genome references
-    load_igenomes      = true
     fasta              = "https://raw.githubusercontent.com/nf-core/test-datasets/rnaseq/reference/genome.fasta"
     gtf                = "https://raw.githubusercontent.com/nf-core/test-datasets/rnaseq/reference/genes.gtf.gz"
     gff                = "https://raw.githubusercontent.com/nf-core/test-datasets/rnaseq/reference/genes.gff.gz"