rpm: revert suppressing systemd_post macro (#759)

We don't need to suppress this macro because this macro handles preset,
not restart.

I have confirmed that this macro of the package for RHEL 9 is expanded
as follows.

```bash
if [ $1 -eq 1 ] && [ -x "/usr/lib/systemd/systemd-update-helper" ]; then
    # Initial installation
    /usr/lib/systemd/systemd-update-helper install-system-units fluentd.service || :
fi
```

Signed-off-by: Daijiro Fukuda <[email protected]>

fluent-package/yum/fluent-package.spec.in

@@ -200,15 +200,7 @@ fi
 %systemd_preun @[email protected]
 
 %post
-. %{_sysconfdir}/sysconfig/@SERVICE_NAME@
-echo "post FLUENT_PACKAGE_SERVICE_RESTART: $FLUENT_PACKAGE_SERVICE_RESTART"
-if [ "$FLUENT_PACKAGE_SERVICE_RESTART" = "auto" ]; then
-  echo "Suppress auto restart in auto mode..."
-elif [ "$FLUENT_PACKAGE_SERVICE_RESTART" = "manual" ]; then
-  echo "Suppress auto restart in manual mode ..."
-else
-  %systemd_post @[email protected]
-fi
+%systemd_post @[email protected]
 if [ $1 -eq 1 ]; then
   if [ -d /etc/@COMPAT_PACKAGE_DIR@ -a ! -h /etc/@COMPAT_PACKAGE_DIR@ ]; then
     touch %{v4migration}