packaging: Simplify get_last_modification()

There's no need to pass repo_root_dir to get_last_modification() as the
variable used everywhere is exported from that very same file.

Fixes: #6431

Signed-off-by: Fabiano Fidêncio <fabiano.fidencio@intel.com>

tools/packaging/scripts/lib.sh

@@ -102,11 +102,9 @@ get_kata_hash() {
 	git ls-remote --heads --tags "https://github.com/${project}/${repo}.git" | grep "${ref}" | awk '{print $1}'
 }
 
-# $1 - Repo's root dir
-# $2 - The file we're looking for the last modification
+# $1 - The file we're looking for the last modification
 get_last_modification() {
-	local repo_root_dir="${1}"
-	local file="${2}"
+	local file="${1}"
 
 	# This is a workaround needed for when running this code on Jenkins
 	git config --global --add safe.directory ${repo_root_dir} &> /dev/null