Remove file named '\'

This looks like it was accidental.

Fixes #20253.

pkgs/development/libraries/mpir/\

@@ -1,20 +0,0 @@
-{stdenv, fetchurl}:
-stdenv.mkDerivation rec {
-  name = "mpir-${version}";
-  version = "1";
-  inherit buildInputs;
-  src = fetchurl {
-    url = "http://mpir.org/mpir-${version}.tar.bz2";
-    sha256 = "0000000000000000000000000000000000000000000000000000000000000000";
-  };
-  meta = {
-    inherit version;
-    description = ''A highly optimised library for bignum arithmetic forked from GMP'';
-    license = stdenv.lib.licenses. ;
-    maintainers = [stdenv.lib.maintainers.raskin];
-    platforms = stdenv.lib.platforms.linux;
-    downloadPage = "http://mpir.org/downloads.html";
-    homepage = "http://mpir.org/";
-    updateWalker = true;
-  };
-}