api: modernize is_supported_system checks

prep for dropping older Ubuntu and Debian versions

api

@@ -2545,15 +2545,15 @@ apt.armbian.com")"
   elif cat /proc/version | grep -qi Microsoft || cat /proc/sys/kernel/osrelease | grep -qi WSL || [[ -f "/run/WSL" ]] || [[ -f "/etc/wsl.conf" ]] || [ -n "$WSL_DISTRO_NAME" ]; then
     echo "Pi-Apps is not supported on WSL."
     return 1
-  elif echo "$PRETTY_NAME" | grep -qi 'stretch\|wheezy\|jessie'; then
-    echo "Pi-Apps is not supported on your outdated operating system. Expect many apps to fail. Consider upgrading your operating system."
+  elif ([ "$__os_id" == "Debian" ] || [ "$__os_id" == "Raspbian" ]) && ! printf '%s\n' "10" "$__os_release" | sort -CV ; then
+    echo "Pi-Apps is not supported on your outdated $__os_id $__os_release operating system. Expect many apps to fail. Consider upgrading your operating system."
+    return 1
+  elif [ "$__os_id" == "Ubuntu" ] && ! printf '%s\n' "18.04" "$__os_release" | sort -CV ; then
+    echo "Pi-Apps is not supported on your outdated $__os_id $__os_release operating system. Expect many apps to fail. Consider upgrading your operating system."
     return 1
   elif echo "$PRETTY_NAME" | grep -qi 'manjaro'; then
     echo "Pi-Apps is not supported on Manjaro."
     return 1
-  elif echo "$PRETTY_NAME" | grep -qi 'Ubuntu 16'; then
-    echo "Pi-Apps is not supported on Ubuntu 16."
-    return 1
   elif [[ "$(uname -m)" == armv6* ]]; then
     echo "Pi-Apps is not supported on ARMv6 Raspberry Pi boards. Expect some apps to fail."
     return 1