Don't remove gitlab_data_dir in purge

debian/gitlab.postrm

@@ -85,8 +85,7 @@ case "$1" in
               rm -rf ${gitlab_data_dir}/$i; fi
           done
         fi
-	for i in ${gitlab_log_dir} ${gitlab_cache_path} ${gitlab_pid_path} \
-${gitlab_data_dir}; do
+	for i in ${gitlab_log_dir} ${gitlab_cache_path} ${gitlab_pid_path}; do
 		safely_remove $i
 	done