Union cleanup before release

[mads-bertelsen]

Free-form text area

Please describe what your PR is adding in terms of features or bugfixes:
Tiny pull request with two small fixes:

Fixed issue causing verbal mode of Union master to not compile as a variable was not declared.
Fixed formating in debug printf in Union master.
Removed debug print in union-lib.c function.

Still has few linter outputs related to the mesh component that will be addressed separately.

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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:
OS X

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PR Checklist for contributing to McStas/McXtrace

For a coherent and useful contribution to McStas/McXtrace, please fill in relevant parts of the checklist:

• My contribution includes patches to an existing component file

  • I have used the mcdoc utility and rendered a reasonable documentation page for the component (please attach as screenshot in comments!)
  • I have ensured that basic use of the component is OK (e.g. an instrument using it compiles?)
  • I have used the mctest utility to test one or more instruments making use of the component (please attach mcviewtest report as screenshot in comments)
  • I have used the mcrun --c-lint "linter" and followed advice to remove most / all warnings that are raised

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[willend]

@mads-bertelsen thanks, merging!