Minor upgrade in Genome::Model::Tools::Analysis::Coverage::MergeReadcounts

Minor upgrade in Genome::Model::Tools::Analysis::Coverage::MergeReadcounts

I removed the restriction on the column size in the input variant files,
and to keep the original header line.
Some of the comments say things are removed, and one says the opposite.  This is likely to cause confusion in the future.

Is the intention here to stop doing the `splice`?  If so, it would be better to remove the this line and the comment above it.