Remove unnecessary check on kernel version

kernel version can only be checked after reboot. Moreover, the code `BEFORE_KERNEL_VERSION='{{ build.PinKernelVersion.outputs.stdout }}'` is syntactically wrong because of a typo

Author: hanwen-cluster

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

@@ -342,7 +342,6 @@ phases:
               set -v
               OS='{{ build.OperatingSystemName.outputs.stdout }}'
               PLATFORM='{{ build.PlatformName.outputs.stdout }}'
-              BEFORE_KERNEL_VERSION='{{ build.PinKernelVersion.output.stdout }}'
               # Remove kernel version lock
               if [[ ${!PLATFORM} == RHEL ]]; then
                 yum versionlock delete kernel kernel-core kernel-modules
@@ -361,9 +360,6 @@ phases:
               else
                 apt-mark unhold linux-aws* linux-base* linux-headers* linux-image* 
               fi
-              if [[ "$(uname -a)" != ${!BEFORE_KERNEL_VERSION} ]] ; then
-                echo "Kernel was upgraded from ${!BEFORE_KERNEL_VERSION} to $(uname -a)"
-              fi
               echo "Kernel version unlocked"
 
       - name: KeepSSM