grsecurity: simplify preConfigure

(cherry picked from commit 39db90e)

pkgs/build-support/grsecurity/default.nix

@@ -123,8 +123,7 @@ let
       # additional build inputs for gcc plugins, required by some PaX/grsec features
       nativeBuildInputs = args.nativeBuildInputs ++ (with pkgs; [ gmp libmpc mpfr ]);
 
-      preConfigure = args.preConfigure or "" + ''
-        rm localversion-grsec
+      preConfigure = (args.preConfigure or "") + ''
         echo ${localver grkern} > localversion-grsec
       '';
     };