Remove legacy hand raise lead code path from trials_controller.rb

Summary

Remove the legacy hand raise lead creation code from trials_controller.rb after successful migration to the new Leads::GitlabCom::HandRaisesController.

Prerequisites

• New Leads::GitlabCom::HandRaisesController deployed and stable
• GitLab.com feature flag new_hand_raise_lead_endpoint rolled out to 100%
• Feature flag has been at 100% for at least 2 weeks with no issues
• GitLab.com legacy routing code removed

Implementation Details

Code Removal

From trials_controller.rb:

• Remove create_hand_raise_lead method
• Remove hand raise-specific before_actions (if any)
• Remove hand raise-specific validations
• Remove hand raise-specific helper methods
• Update routes to remove legacy hand raise endpoint

Verification

Before removing code, verify:

• No traffic to legacy endpoint in last 2 weeks (check logs/metrics)
• All GitLab.com instances using new endpoint
• No errors related to hand raise leads in production

Documentation Updates

• Update internal documentation if it references the old endpoint
• Update any API documentation (if applicable)
• Update https://docs.gitlab.com/development/product_qualified_lead_guide/ if needed