admin/delete_crate: Replace raw SQL with diesel subquery builder

[Turbo87]

as suggested by @weiznich. thank you! :)

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 6 lines in your changes missing coverage. Please review.

Project coverage is 89.20%. Comparing base (a488180) to head (c16a56e).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
src/bin/crates-admin/delete_crate.rs	0.00%	6 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #10005   +/-   ##
=======================================
  Coverage   89.19%   89.20%           
=======================================
  Files         295      295           
  Lines       30768    30766    -2     
=======================================
- Hits        27445    27444    -1     
+ Misses       3323     3322    -1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

---

🚨 Try these New Features:

• Flaky Tests Detection - Detect and resolve failed and flaky tests
• JS Bundle Analysis - Avoid shipping oversized bundles