refactor: remove unused assignments from install script (secureblue#2010)

secureblue#2004 removed the code that used these variables

Author: spaceoden

docs/example.butane

@@ -14,7 +14,7 @@ storage:
       contents:
         source: https://raw.githubusercontent.com/secureblue/secureblue/refs/heads/live/files/system/usr/share/secureblue/install_secureblue.sh
         verification:
-          hash: sha256-40f2b8f168b2715f4452d32292c4e099694f3ebd58cd2659aadd599350904833
+          hash: sha256-5854bdffb805e4dab054ff37c8b2740e4e0dfc1d41b4a11dee9093177e84e14c
       mode: 0755
     - path: /opt/run_install_secureblue.sh
       contents:

files/system/usr/share/secureblue/install_secureblue.sh

@@ -10,10 +10,6 @@ then
     exit 1
 fi
 
-version=$(rpm-ostree --version | grep -oP "Version: '\K[^']+" )
-year=$(echo "$version" | cut -d '.' -f 1)
-subversion=$(echo "$version" | cut -d '.' -f 2)
-
 function is_yes {
     case $(echo "$1" | tr '[:upper:]' '[:lower:]') in
         y|yes) return 0;;