feat: Add DeleteCodeQLDatabase for code scanning

[kyungseopk1m]

Fixes #4419

Adds CodeScanningService.DeleteCodeQLDatabase for DELETE /repos/{owner}/{repo}/code-scanning/codeql/databases/{language}.

The endpoint returns 204 with no body, so the method returns (*Response, error) and passes nil to Do, matching RepositoriesService.DeleteHook.

The operation is already present in openapi_operations.yaml, so go generate ./... produces no changes.

One thing worth flagging for a follow up: the scope sentences on the neighboring ListCodeQLDatabases and GetCodeQLDatabase say security_events, but the current OpenAPI description for all three of these operations says repo or public_repo. I left those two alone to keep this PR to a single endpoint.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.54%. Comparing base (34349a8) to head (d9c10fe).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4421   +/-   ##
=======================================
  Coverage   97.54%   97.54%           
=======================================
  Files         194      194           
  Lines       19765    19771    +6     
=======================================
+ Hits        19279    19285    +6     
  Misses        268      268           
  Partials      218      218           

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