include/starpu_sched_ctx.h: fix compilation

include/starpu_sched_ctx.h

@@ -27,9 +27,8 @@ extern "C"
 
 unsigned starpu_sched_ctx_create(const char *policy_name, int *workerids_ctx, int nworkers_ctx, const char *sched_ctx_name);
 
-#ifdef __STARPU_SCHEDULER_H__
+struct starpu_sched_policy;
 unsigned starpu_sched_ctx_create_with_custom_policy(struct starpu_sched_policy *policy, int *workerids, int nworkers, const char *sched_name);
-#endif
 
 unsigned starpu_sched_ctx_create_inside_interval(const char *policy_name, const char *sched_name, int min_ncpus, int max_ncpus, int min_ngpus, int max_ngpus, unsigned allow_overlap);