Deleting supplier validation

[Menendez6]

Describe your changes

I just deleted the validation on Supplier in Swiss regime

Checklist before requesting a review

• I have performed a self-review of my code.
• I have added thorough tests with at least 90% code coverage.
• I've modified or created example GOBL documents the show my changes in use, if appropriate.
• When adding or modifying a tax regime or addon, I've added links to the source of the changes either structured or in the comments.
• I've run go generate . to ensure that Schemas and Regime data are up to date.
• All linter warnings have been reviewed and fixed.
• I've been obsessive with pointer nil checks to avoid panics.
• The CHANGELOG.md has been updated with an overview of my changes.
• Requested a review from @samlown.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.33%. Comparing base (99d792e) to head (1ac0530).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #428      +/-   ##
==========================================
- Coverage   81.34%   81.33%   -0.01%     
==========================================
  Files         231      230       -1     
  Lines       11369    11348      -21     
==========================================
- Hits         9248     9230      -18     
+ Misses       1760     1758       -2     
+ Partials      361      360       -1     

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[samlown]

Seems reasonable. Might be worth adding a test (or leaving the previous ones) to check that it is always possible to create invoices without a supplier tax ID.