Use command from RedHat guide to clean up old kernels

The commands prior to this PR do not work with RHEL9. Therefore, we change the logic to use the command from the verified guide. I discussed the change with Giordano. We didn't have any concern.

Signed-off-by: Hanwen <hanwenli@amazon.com>

Author: hanwen-cluster

cli/src/pcluster/resources/imagebuilder/update_and_reboot.yaml

@@ -243,19 +243,8 @@ phases:
                 yum -y update
 
                 if [[ ${!OS} == "rhel8" ]] || [[ ${!OS} == "rocky8" ]] || [[ ${!OS} == "rhel9" ]] || [[ ${!OS} == "rocky9" ]] ; then
-                  # package-cleanup has changed in RHEL8 and it works differently
-                  # RHEL8 keeps at least 2 kernel for fallback reason https://access.redhat.com/solutions/1227
-                  # The kernel cleanup should be performed manually
-
-                  # get the default kernel for the next boot
-                  LAST_KERNEL_VERSION=$(grubby --default-kernel | sed -e "s/.*-\(4.18.0-.*\).$(uname -m)/\1/g")
-
-                  # get all the installed kernel versions except the one for the next boot
-                  KERNEL_VERSIONS_CLEANUP=$(rpm -q --qf "%{VERSION}-%{RELEASE}\n" kernel | grep -v "$LAST_KERNEL_VERSION")
-                  for VERSION in $KERNEL_VERSIONS_CLEANUP; do
-                    echo "Removing kernel-$VERSION kernel-core-$VERSION kernel-modules-$VERSION"
-                    rpm -e kernel-$VERSION kernel-core-$VERSION kernel-modules-$VERSION;
-                  done
+                  # package-cleanup has changed in RHEL8 and it works differently https://access.redhat.com/solutions/1227
+                  yum remove $(yum repoquery --installonly --latest-limit=-2 -q)
                 else
                   package-cleanup -y --oldkernels --count=1
                 fi