Remove a conditionally unused declaration

The embedded server does not HAVE_PSI_STAGE_INTERFACE.

storage/maria/ha_maria.cc

@@ -355,10 +355,12 @@ static PSI_file_info all_aria_files[]=
   { &key_file_control, "control", PSI_FLAG_GLOBAL}
 };
 
+# ifdef HAVE_PSI_STAGE_INTERFACE
 static PSI_stage_info *all_aria_stages[]=
 {
   & stage_waiting_for_a_resource
 };
+# endif /* HAVE_PSI_STAGE_INTERFACE */
 
 static void init_aria_psi_keys(void)
 {
@@ -379,9 +381,10 @@ static void init_aria_psi_keys(void)
 
   count= array_elements(all_aria_files);
   mysql_file_register(category, all_aria_files, count);
-
+# ifdef HAVE_PSI_STAGE_INTERFACE
   count= array_elements(all_aria_stages);
   mysql_stage_register(category, all_aria_stages, count);
+# endif /* HAVE_PSI_STAGE_INTERFACE */
 }
 #else
 #define init_aria_psi_keys() /* no-op */