release-lib: Remove unused allowTexliveBuilds option

This is dead code since the old monolithic TeXLive was dropped in
da421bc75f.

pkgs/top-level/release-lib.nix

@@ -1,6 +1,5 @@
 { supportedSystems
 , packageSet ? (import ../..)
-, allowTexliveBuilds ? false
 , scrubJobs ? true
 }:
 
@@ -11,7 +10,6 @@ rec {
   # Ensure that we don't build packages marked as unfree.
   allPackages = args: packageSet (args // {
     config.allowUnfree = false;
-    config.allowTexliveBuilds = allowTexliveBuilds;
     config.inHydra = true;
   });