[DAR-5371] Removed NifTI export pixdim scaling

[JBWilkie]

Problem

When exporting annotations from medical files, we need to perform a transformation from millimetre space to pixel space by dividing annotation coordinates by the appropriate pixdim values based on the primary plane. The problem is that currently, we only apply this transformation for NifTI exports, and we want to apply it to all annotation formats. Additionally, the existing transformation does not take the primary plane into account. We assume that the file was axially-acquired since we use pixdim[0] and pixdim[1]

Solution

This PR removes the pixdim scaling from the NifTI exporter. It is being re-applied to all appropriate medical files in backend as part of DAR-5339, where we will introduce handling for non-axially-acquired images as well

Changelog

Removed pixdim scaling from the NifTI exporter as this will be placed into backend directly

[linear]

DAR-5371 Remove `pixdim` scaling from `NifTI` exporter

DAR-5339 `pixdim` scaling not being applied at export time