debian: Remove 'exit 0' in maintainer section scripts to all other debhelpers (if any) to also execute

debian/qubes-core-agent.postinst

@@ -412,7 +412,6 @@ case "${1}" in
                     ;;
             esac
         done
-        exit 0
         ;;
 
     *)

debian/qubes-core-agent.preinst

@@ -57,11 +57,10 @@ if [ "$1" = "install" ] ; then
     }
     usermod -p '' root
     usermod -L user
-    exit 0
 fi
 
 if [ "$1" = "upgrade" ] ; then
-    exit 0
+    true 
 fi
 
 # dh_installdeb will replace this with shell code automatically