docs: remove out-of-scope spec-delta rationale from CHANGELOG [0.8.3]

The changelog entry described spec changes that required no code
changes, which client_requirements.md's changelog rule excludes as
out-of-scope/not-implemented text. Keep only the changes actually
made in this PR.

Author: claude

CHANGELOG.md

@@ -9,11 +9,6 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 
-- Synced against Apify OpenAPI spec `v2-2026-08-27T071624Z`. The spec changes since
-  `v2-2026-08-14T072928Z` (`RequestWithoutId` bundling fix, `CreateActorRequest.pricingInfos`
-  removal, and validation-error autofixes to `ActorNotice`, `StoreListActor.pictureUrl`, the
-  `ErrorType` enum, and two response definitions) do not affect this client's public interface
-  or behavior, so no code changes were required beyond the version bump.
 - Bumped `APISpecVersion` to `v2-2026-08-27T071624Z` and `ClientVersion` to `0.8.3`.
 - Updated `README.md`'s documented `APISpecVersion` example, which was stale by one spec
   version.