Create Plugin: Remove support for Cypress entirely

[sunker]

Since grafana/plugin-e2e and Playwright were introduced in our tooling, Cypress is no longer supported. However, plugins that previously used Cypress have still been receiving new versions of the e2e-selectors package when running the create-plugin update command.

With the upcoming move to updates as migrations, dependency updates will instead be handled by tools like Dependabot or Renovate. Once that PR is merged, we can safely remove all references to grafana/e2e and Cypress from the create-plugin codebase.