Remove Clusters::Applications refs from docs

What does this MR do and why?

Per Remove clusters_applications_* code (#366573 - closed) we are removing code around Clusters::Applications. Tracking issue: Track Clusters::Applications documentation updates (#379146 - closed)

This MR deletes references to Clusters::Applications in these files.

doc/administration/logs/index.md
doc/development/service_ping/usage_data.md
doc/development/service_ping/implement.md
doc/development/kubernetes.md

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #379146 (closed)