[Serve] remove deprecated APIs, CLI flags, and schema fields

[abrarsheikh]

Several Serve APIs still emit deprecation warnings or remain documented as deprecated while remaining functional. Remove them (or complete the migration) so users are not left with dead-end APIs and noisy logs.

Scope / checklist

• Deployment.url: returns None with a deprecation warning — remove entirely.
• version on @serve.deployment: deprecated, logs warning — remove or raise clear error; align with removal policy.
• version in Deployment.options(): same as above.
• route_prefix: marked deprecated in docstring but still works — remove.
• max_concurrent_queries (schema): marked [DEPRECATED], defaults to max_ongoing_requests — drop from schema.
• deploy_mode (schema): deprecated post single-app removal — remove field.
• AutoscalingConfig.metrics_interval_s: deprecated — use RAY_SERVE_REPLICA_AUTOSCALING_METRIC_PUSH_INTERVAL_S instead; remove old field.
• AutoscalingConfig.smoothing_factor: deprecated — replaced by upscaling_factor / downscaling_factor; remove.
• upscale_smoothing_factor / downscale_smoothing_factor: deprecated — remove; use upscaling_factor / downscaling_factor.
• DeploymentMode enum: fully deprecated (@Deprecated), replaced by ProxyLocation — remove class.
• CLI --http-location: deprecated — remove; use --proxy-location.
• HTTPOptions.location: deprecated — remove; use proxy_location.
• HTTPOptions.num_cpus: deprecated with removal warning — remove.
• HTTPOptions.middlewares: deprecated — remove; document FastAPI middleware integration as the path.

Acceptance criteria

• No remaining references to the removed symbols in public API, docs, or schema; tests updated accordingly.

[Vishnu-sai-teja]

@abrarsheikh Can I take this up ?

[abrarsheikh]

Go for it