remove nix files

.envrc

@@ -1 +0,0 @@
-use_nix

shell.nix

@@ -1,17 +0,0 @@
-with import <nixpkgs> {};
-
-stdenv.mkDerivation rec {
-  name = "rust-env";
-  env = buildEnv { name = name; paths = buildInputs; };
-
-  buildInputs = [
-    latest.rustChannels.nightly.rust
-    openssl
-    fish
-    pkg-config
-    protobuf
-  ];
-
-  PROTOC = "${protobuf}/bin/protoc";
-  PROTOC_INCLUDE = "${protobuf}/include";
-}