fix(frontend): コンディショナルロールを手動で割り当てできる導線を削除

[samunohito]

What

admin/user/[userId]の画面からロールをアサインする際、コンディショナルロールが選択肢として表示されてしまっていたのを塞ぎました。

Why

fix #13529

コンディショナルロールはシステムにより自動判定されて割り当てられるロールなので、手動割り当ては意図とそぐわないため

Additional info (optional)

実際に動作確認済み

Checklist

• Read the contribution guide
• Test working in a local environment
• (If needed) Add story of storybook
• (If needed) Update CHANGELOG.md
• (If possible) Add tests

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 18.83%. Comparing base (420365c) to head (f336cfa).
Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
packages/frontend/src/pages/admin-user.vue	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           develop   #15436   +/-   ##
========================================
  Coverage    18.83%   18.83%           
========================================
  Files          768      768           
  Lines       111555   111555           
  Branches      1236     1236           
========================================
  Hits         21013    21013           
  Misses       89951    89951           
  Partials       591      591           

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[mi-gh-maintainer]

Thank you 🙏