refactor(kuma-cp/kds): remove unnecessary function nesting for mapper

[bartsmykla]

Remove function nesting for MapZoneTokenSigningKeyGlobalToPublicKey resource mapper as we were not using any of the provided arguments.

Checklist prior to review

• Link to relevant issue as well as docs and UI issues
  • No relevant issue
• This will not break child repos: it doesn't hardcode values (.e.g "kumahq" as a image registry) and it will work on Windows, system specific functions like syscall.Mkfifo have equivalent implementation on the other OS
  • It won't as it doesn't change the functionality
• Tests (Unit test, E2E tests, manual test on universal and k8s)
  • No new tests, as this is just pure, small refactor, without changes in functionality
• Do you need to update UPGRADE.md?
  • There is no need
• Does it need to be backported according to the backporting policy?
  • There is no need
• Do you need to explicitly set a > Changelog: entry here or add a ci/ label to run fewer/more tests?

Changelog: refactor(kds): remove unnecessary function nesting for MapZoneTokenSigningKeyGlobalToPublicKey resource mapper in kds context