ESS_KVASIR instrument model cleanup

[willend]

Free-form text area

Please describe what your PR is adding in terms of features or bugfixes:

By quick slip of fingers I accidentally merged #2345 from @AmalieFalkenberg this morning…

This PR is to do a minimum polish / brush-over of the included notebook and the generated output instr for integration in the example instr suite.

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Development OS / boundary conditions

Please describe what OS you developed and tested your additions on, and if any special dependencies are required:

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PR Checklist for contributing to McStas/McXtrace

• My contribution includes a new instrument file

  • I have used the mcdoc utility and rendered a reasonable documentation page for the instrument (please attach as screenshot in comments!)
  • I have ensured that basic use of the instrument is OK (e.g. it compiles?)
  • ... and provided reasonable default parameters in that instrument that produce reasonable output
  • ... and maybe even added a %Example: line to describe expected behaviour
  • I have used the mcrun --c-lint "linter" and followed advice to remove most / all warnings that are raised
  • My new instrument is added within the examples hierarchy in a folder in the style of examples/ESS/New_stuff/New_stuff.instr
  • My new instrument has a new, unique filename, not clashing with existing example instruments
  • My new instrument requires a data/input file. If the datafile is specific for my instrument I have left it in the same example folder, but if general use I have placed it in the global data folder.

• My contribution contains something else

  • Explanation is added in free form text above or below the checklist

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