chore(backend): Remove an unused dependency

[woxtu]

What

現在使われていないモジュールを削除します。

Why

不要なインポートが減ると嬉しい。

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

Merging #11405 (820cea9) into develop (8b74d15) will increase coverage by 0.10%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop   #11405      +/-   ##
===========================================
+ Coverage    78.72%   78.83%   +0.10%     
===========================================
  Files          919      919              
  Lines        97706    97705       -1     
  Branches      7837     7864      +27     
===========================================
+ Hits         76920    77025     +105     
+ Misses       20786    20680     -106     

Files Changed	Coverage Δ
packages/backend/src/boot/master.ts	0.00% <ø> (ø)

... and 16 files with indirect coverage changes

[syuilo]

🙏🏻