(MODULES-11339) Removes Debian 9 from install task

Debian 9 ("stretch") hit the end of its LTS support in June 2022
This commit removes Debian 9 (and older) from the installation task.

Author: mhashizume

tasks/install_shell.sh

@@ -619,11 +619,6 @@ case $platform in
   "Debian")
     info "Debian platform! Lets get you a DEB..."
     case $major_version in
-      "5") deb_codename="lenny";;
-      "6") deb_codename="squeeze";;
-      "7") deb_codename="wheezy";;
-      "8") deb_codename="jessie";;
-      "9") deb_codename="stretch";;
       "10") deb_codename="buster";;
       "11") deb_codename="bullseye";;
     esac