docs(nix): remove premature let scope rule

docs/nix.md

@@ -154,41 +154,6 @@ in
 lib.genAttrs hostNames mkHost
 ```
 
-### Keep bindings in the smallest scope
-
-Place a `let` binding inside the expression that consumes it.
-
-Avoid:
-
-```nix
-let
-  hostNames = lib.attrNames hosts;
-in
-{
-  hostSummary = {
-    inherit hostNames;
-    count = lib.length hostNames;
-  };
-  nixosConfigurations = flakeAssembly.mkHosts (self + "/hosts");
-}
-```
-
-Use:
-
-```nix
-{
-  hostSummary =
-    let
-      hostNames = lib.attrNames hosts;
-    in
-    {
-      inherit hostNames;
-      count = lib.length hostNames;
-    };
-  nixosConfigurations = flakeAssembly.mkHosts (self + "/hosts");
-}
-```
-
 ## Standard Library Calls
 
 ### Qualify standard library calls in flake assembly