CRM: Remove React prototype content

[tbradsha]

This removes a concept onboarding item that was added in #29062 behind a feature flag but never was prioritized or expanded, and had no actual functionality. In the spirit of cleaning things up, I'm removing it.

Proposed changes:

Other information:

• Have you written new tests for your changes, if applicable?
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Jetpack product discussion

Does this pull request change what data or activity we track or use?

Testing instructions:

The plugin should still build and the site should still load. This was never active in production.

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[jp-launch-control]

Code Coverage Summary

Coverage changed in 1 file.

File	Coverage	Δ%	Δ Uncovered
projects/plugins/crm/includes/ZeroBSCRM.Core.php	0/980 (0.00%)	0.00%	-2 💚

Full summary · PHP report