Remove pubsub-light and sse-gateway

[MarkEWaite]

Remove pubsub-light and sse-gateway from plugin BOM

Part of Blue Ocean that has already been removed from BOM.

Amends pull request:

• Remove blueocean from bom #6322

Addresses concern from @NotMyFault in #6142 (comment)

Testing done

• Confirmed LINE=weekly PLUGINS=pipeline-graph-view TEST=InjectedTest bash ./local-test.sh passes

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests that demonstrate the feature works or the issue is fixed

[jglick]

#6322 already removed jenkins-design-language, the only other plugin I know of which does not start with the blueocean- prefix, caught I guess because of its group name.

[jglick]

https://ci.jenkins.io/job/Tools/job/bom/job/PR-6686/1/testReport/junit/com.cloudbees.workflow.ui.view/WorkflowStageViewActionTest/pct_pipeline_stage_view_plugin_weekly___testTimezoneRespectedInStageStartTime/ looks unrelated