Logging: Delete backend code for viewing pod logs

Why are we doing this work

In %15.0, we disabled/removed pod logs by moving it behind a feature flag.

⚠ Removal should take place in %15.2 or later.

Tracking issue for all logging removal work: Monitor:Logging Deprecation (#346485 - closed)

Relevant links

• app/controllers/projects/logs_controller.rb
• config/routes/project.rb
• app/services/pod_logs/kubernetes_service.rb
• app/services/pod_logs/elasticsearch_service.rb
• app/services/pod_logs/base_service.rb
• lib/gitlab/elasticsearch/logs/lines.rb
• lib/gitlab/elasticsearch/logs/pods.rb
• .rubocop_todo/layout/line_length.yml
• app/serializers/environment_entity.rb

Implementation plan

1. Delete logging routes/controllers/models, application code

Elastic Stack configuration is out of scope. See Logging: Delete backend code for configuring lo... (#360192 - closed)