Revert "Revert "linux-hardened: Disable GCC_PLUGIN_RANDSTRUCT""

This reverts commit c68e8b0.

RANDSTRUCT currently fails to work with out-of-tree modules, as
evinced by
NixOS@c68e8b0#commitcomment-31850284
and NixOS#53522.

Specifically, loading out-of-tree modules results in modsym version
mismatches, as in
   spl: version magic '4.20.0 SMP mod_unload modversions RANDSTRUCT_PLUGIN
from the issue above.

A working hypothesis is that the randstruct seed is not carried over when
building out-of-tree modules but more investigation is needed here.

Closes NixOS#53522

pkgs/os-specific/linux/kernel/hardened-config.nix

@@ -125,11 +125,6 @@ ${optionalString (versionAtLeast version "4.20") ''
   GCC_PLUGIN_STACKLEAK y # A port of the PaX stackleak plugin
 ''}
 
-${optionalString (versionAtLeast version "4.13") ''
-  GCC_PLUGIN_RANDSTRUCT y # A port of the PaX randstruct plugin
-  GCC_PLUGIN_RANDSTRUCT_PERFORMANCE y
-''}
-
 # Disable various dangerous settings
 ACPI_CUSTOM_METHOD n # Allows writing directly to physical memory
 PROC_KCORE n # Exposes kernel text image layout