drop stderrr for upsc commands

On debian based system, upsc prints "Init SSL without certificate database" which prevents Zabbix from getting the value

zabbix_conf/nut_ups.conf

@@ -7,7 +7,7 @@
 # Units: %
 # Multiplier: Do not use
 # Store Value: As is
-UserParameter=ups.load[*],upsc $1 ups.load
+UserParameter=ups.load[*],upsc $1 ups.load 2>/dev/null
 
 # Description: Nut UPS Battery Charge
 # Type: Agent or Agent (active)
@@ -16,23 +16,23 @@ UserParameter=ups.load[*],upsc $1 ups.load
 # Units: %
 # Multiplier: Do not use
 # Store Value: As is
-UserParameter=ups.battery.charge[*],upsc $1 battery.charge
+UserParameter=ups.battery.charge[*],upsc $1 battery.charge 2>/dev/null
 
 # Description: Nut UPS Status
 # Type: Agent or Agent (active)
 # Key: ups.status[UPS]
 # Type of information: Character
 # Show Value: As is (you can also define a dictionnary OL=>On Line etc...)
-UserParameter=ups.status[*],upsc $1 ups.status
+UserParameter=ups.status[*],upsc $1 ups.status 2>/dev/null
 
 # Description: Nut UPS Model
 # Type: Agent or Agent (active)
 # Key: ups.model[UPS]
 # Type of information: Text
-UserParameter=ups.model[*],upsc $1 ups.model
+UserParameter=ups.model[*],upsc $1 ups.model 2>/dev/null
 
 # UPS discovery
 UserParameter=hardware.ups.discovery[*],/var/lib/zabbix/bin/disco_nut_ups $1
 
 # This is a new, more generic nut ups UserParameter
-UserParameter=hardware.ups[*],upsc $1 $2
+UserParameter=hardware.ups[*],upsc $1 $2 2>/dev/null