rust: remove beta and nightly releases

nixpkgs is for stable software. If you want beta and nightly, use the
nixpkgs-mozilla overlay.

pkgs/top-level/all-packages.nix

@@ -6175,33 +6175,11 @@ with pkgs;
     inherit (darwin) apple_sdk;
   };
 
-  rustRegistry = callPackage ./rust-packages.nix { };
-
-  rust = rustStable;
-  rustStable = callPackage ../development/compilers/rust {
-    inherit (llvmPackages_4) llvm;
-  };
-  rustBeta = lowPrio (recurseIntoAttrs (callPackage ../development/compilers/rust/beta.nix {}));
-
-  rustNightly = rustBeta;
+  # For beta and nightly releases use the nixpkgs-mozilla overlay
+  rust = callPackage ../development/compilers/rust { };
+  inherit (rust) cargo rustc;
 
-  # rust support in nixpkgs isn't yet well maintained enough for us to
-  # pretend to support nightlies in a meaningful way.
-
-  # rustNightly = lowPrio (recurseIntoAttrs (callPackage ../development/compilers/rust/nightly.nix {
-  #   rustPlatform = recurseIntoAttrs (makeRustPlatform rustBeta);
-  # }));
-
-  rustNightlyBin = lowPrio (callPackage ../development/compilers/rust/nightlyBin.nix {
-     buildRustPackage = callPackage ../build-support/rust {
-       rust = rustNightlyBin;
-     };
-  });
-
-  cargo = rust.cargo;
-  rustc = rust.rustc;
-
-  cargo-edit = callPackage ../tools/package-management/cargo-edit { };
+  rustRegistry = callPackage ./rust-packages.nix { };
 
   rustPlatform = recurseIntoAttrs (makeRustPlatform rust);
 
@@ -6224,6 +6202,8 @@ with pkgs;
 
     });
 
+  cargo-edit = callPackage ../tools/package-management/cargo-edit { };
+
   rainicorn = callPackage ../development/tools/rust/rainicorn { };
   rustfmt = callPackage ../development/tools/rust/rustfmt { };
   rustracer = callPackage ../development/tools/rust/racer { };