mesa: cleanup: rm defunct glx-rts & sysfs flags, grsec/PaX patch

Config log:

```
configure: WARNING: unrecognized options: --disable-glx-rts, --enable-sysfs
```

pkgs/development/libraries/mesa/default.nix

@@ -4,7 +4,6 @@
 , llvmPackages, libffi, libomxil-bellagio, libva-minimal
 , libelf, libvdpau, valgrind-light, python2
 , libglvnd
-, grsecEnabled ? false
 , enableRadv ? true
 , galliumDrivers ? null
 , driDrivers ? null
@@ -87,7 +86,6 @@ let self = stdenv.mkDerivation {
   #  revive ./dricore-gallium.patch when it gets ported (from Ubuntu), as it saved
   #  ~35 MB in $drivers; watch https://launchpad.net/ubuntu/+source/mesa/+changelog
   patches = [
-    ./glx_ro_text_segm.patch # fix for grsecurity/PaX
     ./symlink-drivers.patch
     ./missing-includes.patch # dev_t needs sys/stat.h, time_t needs time.h, etc.-- fixes build w/musl
   ];
@@ -112,7 +110,6 @@ let self = stdenv.mkDerivation {
       ("--with-vulkan-drivers=" +
         builtins.concatStringsSep "," vulkanDrivers))
   ++ [
-    (enableFeature grsecEnabled "glx-rts")
     (enableFeature stdenv.isLinux "dri3")
     (enableFeature stdenv.isLinux "nine") # Direct3D in Wine
     "--enable-libglvnd"
@@ -131,7 +128,6 @@ let self = stdenv.mkDerivation {
     "--enable-xvmc"
     "--enable-vdpau"
     "--enable-shared-glapi"
-    "--enable-sysfs"
     "--enable-llvm-shared-libs"
     "--enable-omx-bellagio"
     "--enable-va"

pkgs/development/libraries/mesa/glx_ro_text_segm.patch

@@ -1,25 +0,0 @@
-diff --git a/configure.ac b/configure.ac
-index 5068913..3d4271e 100644
---- a/configure.ac
-+++ b/configure.ac
-@@ -429,6 +429,20 @@ AC_SUBST([GLESv2_LIB_GLOB])
- AC_SUBST([VG_LIB_GLOB])
- AC_SUBST([GLAPI_LIB_GLOB])
- 
-+
-+dnl readonly text segment on x86 hardened platforms
-+AC_ARG_ENABLE([glx_rts],
-+    [AS_HELP_STRING([--enable-glx-rts],
-+        [on x86, use a readonly text segment for libGL @<:@default=disabled@:>@])],
-+    [enable_glx_rts="$enableval"],
-+    [enable_glx_rts=no])
-+if test "x$enable_glx_rts" = xyes; then
-+    DEFINES="$DEFINES -DGLX_X86_READONLY_TEXT"
-+else
-+    enable_glx_rts=no
-+fi
-+
-+
- dnl
- dnl Arch/platform-specific settings
- dnl

pkgs/top-level/all-packages.nix

@@ -10952,9 +10952,6 @@ with pkgs;
   libGLDarwinOr = alternative: if stdenv.isDarwin then libGLDarwin else alternative;
 
   mesa_noglu = callPackage ../development/libraries/mesa {
-    # makes it slower, but during runtime we link against just mesa_drivers
-    # through /run/opengl-driver*, which is overriden according to config.grsecurity
-    # grsecEnabled = true; # no more support in nixpkgs ATM
     llvmPackages = llvmPackages_6;
   };