Drop ubuntu 18.04

Signed-off-by: Yury Bushmelev <jay4mail@gmail.com>

Author: jay7x

metadata.json

@@ -51,7 +51,6 @@
     {
       "operatingsystem": "Ubuntu",
       "operatingsystemrelease": [
-        "18.04",
         "22.04",
         "24.04"
       ]