Deprecate any Claude 2_1 model usage

Deprecate Claude 2.1 in GitLab Rails and AI Gateway Client

Problem Statement

We currently support Claude 2.1 in both our GitLab Rails application and AI gateway client. This legacy support increases maintenance overhead and complicates our codebase, potentially hindering our ability to quickly iterate and improve our AI-powered features.

Proposal

We propose to remove support for Claude 2.1 in both GitLab Rails and the AI gateway client. This aligns with our epic "Unification of the code for AI Tools" and will streamline our development process by focusing on the Claude 3 family of models.

Acceptance Criteria

• All references to Claude 2.1 are removed from GitLab Rails codebase
• All references to Claude 2.1 are removed from AI gateway client
• Documentation is updated to reflect the removal of Claude 2.1 support
• The AI Gateway Overview dashboard no longer shows any Claude 2.1 usage (https://dashboards.gitlab.net/d/ai-gateway-main/ai-gateway3a-overview)
• All existing AI features continue to function correctly with Claude 3 family models