make-bootstrap-tools.nix: drop libelf.so from tootstrap tarballs

gcc stopped using libelf in commit 48215350c24 ("re PR lto/46273 (Failed
to bootstrap)") around 2010, before gcc-4.6.0.

Bootstrap tools don't use it either.

pkgs/stdenv/linux/make-bootstrap-tools.nix

@@ -152,7 +152,6 @@ in with pkgs; rec {
         cp -d ${mpfr.out}/lib/libmpfr*.so* $out/lib
         cp -d ${libmpc.out}/lib/libmpc*.so* $out/lib
         cp -d ${zlib.out}/lib/libz.so* $out/lib
-        cp -d ${libelf}/lib/libelf.so* $out/lib
 
       '' + lib.optionalString (stdenv.hostPlatform != stdenv.buildPlatform) ''
         # These needed for cross but not native tools because the stdenv