bison: update to version 2.6.5

This update fixes the grub-2.0 warning issue that was worked around in commit
4f5e655b36. Consequently, that patch is no longer
needed.

pkgs/tools/misc/grub/2.0x.nix

@@ -49,17 +49,10 @@ stdenv.mkDerivation rec {
        sed -i '/gets is a security hole/d' grub-core/gnulib/stdio.in.h
     '';
 
-  # Source code generated by bison 2.6.4 contains pragmas that trigger
-  # warnings when built with -Wunknown-pragmas. Since Grub compiles with
-  # -Werror, this causes the build to fail. We work around this issue by
-  # ignoring pragma-related warnings, but clearly it would be better if
-  # Bison wouldn't trigger that issue in the first place. A bug report
-  # has been sent.
   prePatch =
     '' gunzip < "${unifont_bdf}" > "unifont.bdf"
        sed -i "configure" \
-           -e "s|/usr/src/unifont.bdf|$PWD/unifont.bdf|g" \
-           -e "s|-Wunknown-pragmas|-Wno-pragmas|g"
+           -e "s|/usr/src/unifont.bdf|$PWD/unifont.bdf|g"
     '';
 
   configureFlags =