use command -v instead of test -x

debian/postrm

@@ -60,7 +60,7 @@ case "$1" in
         rm -rf ${gitlab_data_dir}
         if [ ! -z "${gitlab_user}" ]; then
             # Do only if gitlab_user is set
-            if [ -x /usr/bin/dropdb ]; then
+            if command -v dropdb >/dev/null; then
                 echo "Removing Database: gitlab_production"
                 su ${gitlab_user} -c 'psql gitlab_production -c ""' && su postgres -c "dropdb gitlab_production"
             else