Remove StandardOutput, StandardError in service (#390)

systemd 249 (used in Ubuntu 22.04 LTS) throws the following error:

/etc/systemd/system/stalwart-mail.service:16: Standard output type
syslog is obsolete, automatically updating to journal. Please update
your unit file, and consider removing the setting altogether.

/etc/systemd/system/stalwart-mail.service:17: Standard output type
syslog is obsolete, automatically updating to journal. Please update
your unit file, and consider removing the setting altogether.

This is caused by StandardOutput=syslog and StandardError=syslog found
in install.sh, which are as the error suggests obsolete options that
should not be used.[1] They have "correct" settings in
stalwart-mail.service, but these settings are also the implicit
default, which means they are not necessary.[1]

This was patched in systemd #15812 in May, 2020.[2]

I have tested this by simply removing the values in
/etc/systemd/system/stalwart-mail.service on my server, running
'daemon-reload' and restarting the service, then confirming that logs
are still being written to journalctl as well as /opt/stalwart-mail/logs

[1]: <https://github.com/systemd/systemd/issues/15807#issuecomment-628528787>
[2]: <https://github.com/systemd/systemd/pull/15812>

install.sh

@@ -147,8 +147,6 @@ Restart=on-failure
 RestartSec=5
 ExecStart=__PATH__/bin/stalwart-mail --config=__PATH__/etc/config.toml
 PermissionsStartOnly=true
-StandardOutput=syslog
-StandardError=syslog
 SyslogIdentifier=stalwart-mail
 
 [Install]

resources/systemd/stalwart-mail.service

@@ -13,8 +13,6 @@ Restart=on-failure
 RestartSec=5
 ExecStart=__PATH__/bin/stalwart-mail --config=__PATH__/etc/config.toml
 PermissionsStartOnly=true
-StandardOutput=journal
-StandardError=journal
 SyslogIdentifier=stalwart-mail
 
 [Install]