Fix comment in injection_point.c

InjectionPointEntry->name was described as a hash key, which was fine
when introduced in d86d20f0ba79, but it is not now.

Oversight in 86db52a5062a, that has changed the way injection points are
stored in shared memory from a hash table to an array.

Backpatch-through: 17

src/backend/utils/misc/injection_point.c

@@ -59,7 +59,7 @@ typedef struct InjectionPointEntry
 	 */
 	pg_atomic_uint64 generation;
 
-	char		name[INJ_NAME_MAXLEN];	/* hash key */
+	char		name[INJ_NAME_MAXLEN];	/* point name */
 	char		library[INJ_LIB_MAXLEN];	/* library */
 	char		function[INJ_FUNC_MAXLEN];	/* function */