Remove nix-related patches and files

Everything has now been moved to
https://gitlab.redox-os.org/redox-os/redox-nix :)

mk/prefix.mk

@@ -92,8 +92,6 @@ $(PREFIX)/gcc-install: $(PREFIX)/gcc-install.tar.gz
 	rm -rf "$@.partial" "$@"
 	mkdir -p "$@.partial"
 	tar --extract --file "$<" --directory "$@.partial" --strip-components=1
-	[ -n "$$NIX_INTERPRETER" ] && find "$@.partial" -executable -type f -exec \
-		patchelf --set-interpreter "$$NIX_INTERPRETER" "{}" \;
 	touch "$@.partial"
 	mv "$@.partial" "$@"
 

shell.nix

-{ pkgs ? import <nixpkgs> {} }:
-
-pkgs.mkShell rec {
-  hardeningDisable = [ "all" ];
-
-  # used in mk/prefix.mk to patch interpreter when PREFIX_BINARY=1
-  NIX_INTERPRETER = "${pkgs.stdenv.cc.libc}/lib/ld-linux-x86-64.so.2";
-
-  LIBRARY_PATH = pkgs.lib.makeLibraryPath [
-    pkgs.gcc-unwrapped pkgs.stdenv.cc.libc
-    (toString prefix/x86_64-unknown-redox)
-  ];
-  LD_LIBRARY_PATH = LIBRARY_PATH;
-
-  nativeBuildInputs = with pkgs; [ gnumake cmake nasm pkgconfig gcc automake autoconf bison gperf qemu rustup ];
-  buildInputs = with pkgs; [ fuse openssl gettext libtool flex libpng perl perlPackages.HTMLParser ];
-
-  shellHook = ''
-    export PATH="/run/wrappers/bin:$PATH"
-  '';
-}