Remove unused routine from normal_distribution_mod.f90

[hkershaw-brown]

Description:

Removed unused routine from normal_distribution_mod.f90
Why?

• we've had a couple of users be tripped up on this warning #6843 while troubleshooting other problems
• broken windows, innit?

Fixes issue

fixes #736

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Documentation changes needed?

• My change requires a change to the documentation.
  • I have updated the documentation accordingly.

Tests

Please describe any tests you ran to verify your changes.

Build everything in DART on "unused-routine" branch:
https://github.com/NCAR/DART/actions/runs/11613730959

note the GOES build fails because the container is linking to rttov12 not rttov13 (NCAR/DART-containers#1).

Checklist for merging

• Updated changelog entry
• Documentation updated
• Update conf.py

Checklist for release

• Merge into main
• Create release from the main branch with appropriate tag
• Delete feature-branch

Testing Datasets

• Dataset needed for testing available upon request
• Dataset download instructions included
• No dataset needed

[mjs2369]

Clean removal