treewide: use ${stdenv.shell} instead of /bin/sh where possible

pkgs/tools/archivers/rpmextract/default.nix

@@ -10,6 +10,7 @@ stdenv.mkDerivation rec {
   script = substituteAll {
     src = ./rpmextract.sh;
     inherit rpm cpio;
+    inherit (stdenv) shell;
   };
 
   meta = with stdenv.lib; {

pkgs/tools/archivers/rpmextract/rpmextract.sh

@@ -1,4 +1,4 @@
-#!/bin/sh -e
+#!@shell@ -e
 
 if [ "$1" = "" ]; then
   echo "usage: rpmextract package_name..." 1>&2