linuxPackages.phc-intel: remove use of features.grsecurity

I believe this is the final reference to features.grsecurity.
See also e6c65ecb12c58cfa043d9cfa6db31b9920603588

pkgs/os-specific/linux/phc-intel/default.nix

···
 assert stdenv.isLinux;
 # Don't bother with older versions, though some might even work:
 assert stdenv.lib.versionAtLeast kernel.version "4.10";
-# Disable on grsecurity kernels, which break module building:
-assert !kernel.features ? grsecurity;
 
 let
   release = "0.4.0";