Remove "subscriptions is a significant change" sentence (#983)

Co-authored-by: Benjie <benjie@jemjie.com>
Co-authored-by: Roman Ivantsov <roman.ivantsov@microsoft.com>

Author: 3 people

spec/Section 6 -- Execution.md

@@ -224,9 +224,8 @@ must receive no more events from that event stream.
 
 **Supporting Subscriptions at Scale**
 
-Supporting subscriptions is a significant change for any GraphQL service. Query
-and mutation operations are stateless, allowing scaling via cloning of GraphQL
-service instances. Subscriptions, by contrast, are stateful and require
+Query and mutation operations are stateless, allowing scaling via cloning of
+GraphQL service instances. Subscriptions, by contrast, are stateful and require
 maintaining the GraphQL document, variables, and other context over the lifetime
 of the subscription.