Remove superfluous condition statement on existence of vcf parameter in segmentationPSCBS

[tinyheero]

This PR removes the following superfluous condition statements from the segmentationPSCBS() function:

if (!is.null(vcf)) {

Before this condition statement is run, the function .PSCBSinput() is run to generate inputs for PSCBS. This function has the following condition statement:

if (is.null(vcf)) {
    .stopUserError("segmentationPSCBS requires VCF file.")
}

As such, checking for whether the parameter vcf is set has already happened upstream.

Additionally, this condition statement determines where .pruneByHclust() is run. But PSCBS has already been run potentially 2 times before this function is run. Since, PSCBS can't be run without a VCF file (more specifically BAF values) this condition statement will always evaluate to TRUE making it both confusing and superfluous.

[lima1]

Good catch, thank you!