stm class: Remove an unused function

Fix the following clang warning:

drivers/hwtracing/stm/policy.c:60:21: warning: unused function
'stp_policy_node_name' [-Wunused-function].
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20210414171251.14672-2-alexander.shishkin@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hwtracing/stm/policy.c

@@ -57,11 +57,6 @@ void stp_policy_node_get_ranges(struct stp_policy_node *policy_node,
 	*cend	= policy_node->last_channel;
 }
 
-static inline char *stp_policy_node_name(struct stp_policy_node *policy_node)
-{
-	return policy_node->group.cg_item.ci_name ? : "<none>";
-}
-
 static inline struct stp_policy *to_stp_policy(struct config_item *item)
 {
 	return item ?