fix(frontend): Remove undefined styles

[woxtu]

What

コンポーネント内の未定義なスタイルを削除します。

Why

ビルドするときに出る次の警告を解決したい：

Undefined style detected: $style.root (in MkAd)
Undefined style detected: $style.captcha (in XPassword)
Undefined style detected: $style.captcha (in XPassword)
Undefined style detected: $style.captcha (in XPassword)
Undefined style detected: $style.captcha (in XPassword)
Undefined style detected: $style.captcha (in XPassword)
Undefined style detected: $style.accountSelectorRoot (in MkAuthConfirm)
Undefined style detected: $style.accountSelectorRoot (in MkAuthConfirm)
Undefined style detected: $style.root (in XAbuseReport)

Additional info (optional)

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 11.11111% with 8 lines in your changes missing coverage. Please review.

Project coverage is 19.39%. Comparing base (b107371) to head (62bac82).
Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
...ages/frontend/src/components/MkSignin.password.vue	0.00%	5 Missing ⚠️
packages/frontend/src/components/MkAuthConfirm.vue	0.00%	2 Missing ⚠️
packages/frontend/src/components/MkAbuseReport.vue	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           develop   #14858       +/-   ##
============================================
- Coverage    39.51%   19.39%   -20.13%     
============================================
  Files         1557      724      -833     
  Lines       196659   103242    -93417     
  Branches      3609      992     -2617     
============================================
- Hits         77709    20022    -57687     
+ Misses      118346    82669    -35677     
+ Partials       604      551       -53     

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[syuilo]

🙏🏻