chore: delete unused ChannelsService

[anatawa12]

What

#16985 で使わなくなってたんですが、ファイルの削除を忘れてたのでそれです。

Why

シンプルに無駄。downstreamが誤解する

Additional info (optional)

内部的な変更なので no changelog entry

search result (定義1件のみ)

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

[github-actions]

このPRによるapi.jsonの差分
差分はありません。
Get diff files from Workflow Page

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 63.51%. Comparing base (a025209) to head (9b5559b).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff              @@
##           develop   #17218       +/-   ##
============================================
+ Coverage    13.90%   63.51%   +49.61%     
============================================
  Files          241     1160      +919     
  Lines        11690   115912   +104222     
  Branches      3951     8346     +4395     
============================================
+ Hits          1625    73620    +71995     
- Misses        7901    40087    +32186     
- Partials      2164     2205       +41     

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[github-actions]

Backend memory usage comparison

Before GC

Metric	base (MB)	head (MB)	Diff (MB)	Diff (%)
VmRSS	322.66 MB	330.89 MB	+8.23 MB	+2.55%
VmHWM	322.66 MB	330.89 MB	+8.23 MB	+2.55%
VmSize	23115.74 MB	23124.71 MB	+8.96 MB	+0.03%
VmData	1385.99 MB	1395.04 MB	+9.04 MB	+0.65%

After GC

Metric	base (MB)	head (MB)	Diff (MB)	Diff (%)
VmRSS	322.66 MB	330.93 MB	+8.26 MB	+2.56%
VmHWM	322.66 MB	330.93 MB	+8.26 MB	+2.56%
VmSize	23115.74 MB	23124.79 MB	+9.04 MB	+0.03%
VmData	1385.99 MB	1395.12 MB	+9.13 MB	+0.65%

After Request

Metric	base (MB)	head (MB)	Diff (MB)	Diff (%)
VmRSS	323.06 MB	331.33 MB	+8.26 MB	+2.55%
VmHWM	323.06 MB	331.33 MB	+8.26 MB	+2.55%
VmSize	23115.83 MB	23124.87 MB	+9.04 MB	+0.03%
VmData	1386.07 MB	1395.20 MB	+9.12 MB	+0.65%

See workflow logs for details