dispvm: don't use perl to decode base64-encoded script

This looks like an overkill. And more importantly - required modules are
not installed by default, making it impossible to use in default minimal
template.

Fixes QubesOS/qubes-issues#1610

init/functions

@@ -38,7 +38,7 @@ possibly_run_save_script() {
     ENCODED_SCRIPT=$(qubesdb-read /qubes-save-script)
     if [ -z "$ENCODED_SCRIPT" ] ; then return ; fi
     tmpfile=$(mktemp /tmp/qubes-save-script.XXXXXXXXX)
-    echo $ENCODED_SCRIPT|perl -e 'use MIME::Base64 qw(decode_base64); local($/) = undef;print decode_base64(<STDIN>)' >"$tmpfile"
+    echo $ENCODED_SCRIPT|base64 -d >"$tmpfile"
     chmod 755 "$tmpfile"
     DISPLAY=:0 su - user -c "$tmpfile"
     ret=$?