Remove metrics for SSE feature

What does this MR do and why?

Remove all metrics, usage_data, etc for Static Site Editor feature. The implementation of the feature has already been removed in Remove all SSE references [RUN ALL RSPEC] [RUN ... (!87221 - merged)

Resolves: #362977 (closed) Related: Remove Static Site Editor code (#352505 - closed)

See also: https://docs.gitlab.com/ee/development/service_ping/metrics_lifecycle.html#remove-a-metric

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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.
• As requested in Step 5 of https://docs.gitlab.com/ee/development/service_ping/metrics_lifecycle.html#remove-a-metric, this issue (https://gitlab.com/gitlab-data/analytics/-/issues/12899+) is to ensure these metrics are not used in any Sisense dashboards or other places that need to be cleaned up.