Update spans-and-attributes.mdx

Also remove cold start since we do not have that info yet

Author: jmorrell-cloudflare

src/content/docs/workers/observability/traces/spans-and-attributes.mdx

@@ -79,9 +79,7 @@ Cloudflare Workers provides automatic tracing instrumentation **out of the box**
 - `cloudflare.outcome`
 - `cloudflare.cpu_time`
 - `cloudflare.wall_time`
-- `cloudflare.cold_start_ms`
 - `faas.trigger`
-- `faas.cold_start`
 - `cloudflare.ray_id`
 - `cloudflare.verified_bot_category`
 - `cloudflare.asn`