gawk: Remove unnecessary ‘gawk-<version>’ copy

This saves > 600 KiB.

pkgs/tools/text/gawk/default.nix

@@ -8,8 +8,6 @@ stdenv.mkDerivation rec {
     sha256 = "0hin2hswbbd6kd6i4zzvgciwpl5fba8d2s524z8y5qagyz3x010q";
   };
 
-  patches = [];
-
   doCheck = !stdenv.isCygwin; # XXX: `test-dup2' segfaults on Cygwin 6.1
 
   buildInputs = [ libsigsegv ]
@@ -20,6 +18,8 @@ stdenv.mkDerivation rec {
       # only darwin where reported, seems OK on non-chrooted Fedora (don't rebuild stdenv)
     ++ stdenv.lib.optional (!readlineSupport && stdenv.isDarwin) "--without-readline";
 
+  postInstall = "rm $out/bin/gawk-*";
+
   meta = {
     homepage = http://www.gnu.org/software/gawk/;
     description = "GNU implementation of the Awk programming language";