Remove `threat insights` and `container security` dev dashboards from threat...

Why is this change being made?

Remove Threat Insights and Container Security Development dashboards from the group sections under https://about.gitlab.com/handbook/engineering/development/performance-indicators/threat-management/#threat-insights-group

Team members will have Threat Management as the job title speciality instead of Threat Insights and Container Security

Slack conversation: https://gitlab.slack.com/archives/C01236LHF1A/p1602025013005500

Review link: https://lmai1-master-patch-94182.about.gitlab-review.app/handbook/engineering/development/performance-indicators/threat-management/index.html

Author Checklist

• Provided a concise title for the MR
• Added a description to this MR explaining the reasons for the proposed change, per say-why-not-just-what
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