meta-phosphor: slpd-lite: remove env call from service file

We are suppose to use direct executable calls in service files
rather than indirections through /bin/env (See Anti-patterns).

Tested:
```
root@witherspoon:~# systemctl status slpd-lite
* slpd-lite.service - Lightweight SLP Server
     Loaded: loaded (/lib/systemd/system/slpd-lite.service; enabled; preset: enabled)
     Active: active (running) since Thu 2023-04-06 16:32:29 UTC; 58s ago
   Main PID: 205 (slpd)
        CPU: 70ms
     CGroup: /system.slice/slpd-lite.service
             `-205 /usr/sbin/slpd

Apr 06 16:32:29 witherspoon systemd[1]: Started Lightweight SLP Server.
```

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I08c0eaff39798fb3095d816389a8752b343164e7
diff --git a/meta-phosphor/recipes-phosphor/interfaces/slpd-lite/slpd-lite.service b/meta-phosphor/recipes-phosphor/interfaces/slpd-lite/slpd-lite.service
index 4cbeb84..5181b76 100644
--- a/meta-phosphor/recipes-phosphor/interfaces/slpd-lite/slpd-lite.service
+++ b/meta-phosphor/recipes-phosphor/interfaces/slpd-lite/slpd-lite.service
@@ -4,7 +4,7 @@
 After=network.target
 
 [Service]
-ExecStart=/usr/bin/env slpd
+ExecStart=/usr/sbin/slpd
 SyslogIdentifier=slpd
 Restart=always