Update build.func

Remove Ubuntu 18.04, which will reach EOL on April 30, 2023

misc/build.func

@@ -114,8 +114,7 @@ exit-script() {
 
 advanced_settings() {
   if [ "$var_os" == "ubuntu" ]; then
-    if var_version=$(whiptail --title "UBUNTU VERSION" --radiolist "Choose Version" 10 58 4 \
-      "18.04" "Bionic" OFF \
+    if var_version=$(whiptail --title "UBUNTU VERSION" --radiolist "Choose Version" 10 58 3 \
       "20.04" "Focal" ON \
       "22.04" "Jammy" OFF \
       "22.10" "Kinetic" OFF \