test(cloudflare): remove redundant mcp-endpoint tests

Delete mcp-endpoint.test.ts as it tested third-party library behavior
(@cloudflare/workers-oauth-provider), not our code.

Per docs/testing.md: "Don't test third-party library behavior".

The tests verified:
- OAuthProvider returns 401 for unauthenticated requests
- OAuthProvider returns 401 for invalid tokens
- OAuthProvider exposes OAuth discovery metadata
- OAuthProvider handles dynamic client registration

mcp-handler.test.ts already covers our authentication logic:
- Handler rejects requests without auth context
- Handler rejects legacy tokens without grantedSkills
- Handler rejects tokens with no valid skills

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: dcramer