controllers/krate/delete: Adjust HTTP status code

[Turbo87]

DELETE endpoints are supposed to return "204 No Content" upon successful deletion, unless the response contains an entity, which is not the case here.

see https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/DELETE#successfully_deleting_a_resource

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.58%. Comparing base (7541baf) to head (2a3755a).
Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #10169   +/-   ##
=======================================
  Coverage   89.57%   89.58%           
=======================================
  Files         295      295           
  Lines       31690    31694    +4     
=======================================
+ Hits        28386    28392    +6     
+ Misses       3304     3302    -2     

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