install: Drop Lightspeed CustomResourceDefinitions (Proposal, etc.)

These are now conveniently installed in test clusters via [1], so we
can demo tech-preview Proposal creation with the agentic Lightspeed
operator installed, without having to install the CRDs ourselves.
Reverts 4936d65 (OTA-1965: Add Lightspeed
CustomResourceDefinitions, 2026-04-21, #1380).

[1]: https://github.com/openshift/lightspeed-agentic-operator/tree/main/hack/quickstart

Author: wking