chore: small patches before release

[ycexiao]

• chore: move the position of license identifier
• chore: remove the skill

What problem does this PR address?

(1) python -m build gives

WARNING License classifiers are deprecated.
!!
        ********************************************************************************
        Please consider removing the following classifiers in favor of a SPDX license expression:
        License :: OSI Approved :: BSD License
        See https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#license for details.
        ********************************************************************************

(2) the skill is moved to diffpy/cmi-agent-skills#3, but there is still a markdown file in this repo

What should the reviewer(s) do?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.24%. Comparing base (a03f694) to head (d09c7f5).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #40   +/-   ##
=======================================
  Coverage   98.24%   98.24%           
=======================================
  Files           8        8           
  Lines         626      626           
=======================================
  Hits          615      615           
  Misses         11       11           

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[ycexiao]

@sbillinge, it's ready for review.