Clean up the changelog

Author: grahamc

doc/manual/source/release-notes-determinate/v3.15.1.md

@@ -3,8 +3,13 @@
 * Based on [upstream Nix 2.33.0](../release-notes/rl-2.33.md).
 
 ## What's Changed
-* Bring back the free alpha by @grahamc in [DeterminateSystems/nix-src#305](https://github.com/DeterminateSystems/nix-src/pull/305)
-* Replace substitutable hashes with unlilkey to substitute hashes by @grahamc in [DeterminateSystems/nix-src#306](https://github.com/DeterminateSystems/nix-src/pull/306)
+Users reported the v3.15.0 tarball could not be fetched in a fixed-output derivation due to current stdenv paths present in the documentation. This release eliminated those paths.
+
+PR: [DeterminateSystems/nix-src#306](https://github.com/DeterminateSystems/nix-src/pull/306)
+
+Additionally, this change re-enables CodeRabbit's code review on our changes. CodeRabit was disabled by the upstream project, and we inadvertently included that change.
+
+PR: [DeterminateSystems/nix-src#305](https://github.com/DeterminateSystems/nix-src/pull/305)
 
 
 **Full Changelog**: [v3.15.0...v3.15.1](https://github.com/DeterminateSystems/nix-src/compare/v3.15.0...v3.15.1)