Remove by GUID instead of MSI path

So upgrades/downgrades work as expected

packages/zabbix_agent.xml

@@ -26,7 +26,8 @@
         <remove cmd='%COMSPEC% /C sc stop "Zabbix Agent"'>
             <exit code="any" />
         </remove>
-        <remove cmd='msiexec /qn /norestart /x "%MSI%"' />
+        <!-- Remove by GUID -->
+        <remove cmd='msiexec /qn /norestart /x "{BFF41D43-5F14-4B3C-AFD1-CC91F673E88E}"' />
         <remove cmd='netsh advfirewall firewall del rule name="Zabbix Agent"' />
 
     </package>