netbsd.install: Use `writeShellScript`

pkgs/os-specific/bsd/netbsd/default.nix

···
 , buildPackages, splicePackages, newScope
 , bsdSetupHook, makeSetupHook, fetchcvs, groff, mandoc, byacc, flex
 , zlib
-, writeScript, writeText, runtimeShell, symlinkJoin
+, writeShellScript, writeText, runtimeShell, symlinkJoin
 }:
 
 let
···
 
   # HACK: to ensure parent directories exist. This emulates GNU
   # install’s -D option. No alternative seems to exist in BSD install.
-  install = let binstall = writeScript "binstall" ''
-    #!${runtimeShell}
+  install = let binstall = writeShellScript "binstall" ''
     set -eu
     for last in "$@"; do true; done
     mkdir -p $(dirname $last)