CLEANUP: pools: declare dummy pool functions to remove some ifdefs

By having a pair of dummy pool_get_from_cache() and pool_put_to_cache()
we can remove some ugly ifdefs, so let's do this. We've already done it
for the shared cache.
diff --git a/include/haproxy/pool.h b/include/haproxy/pool.h
index d9dc527..54ec933 100644
--- a/include/haproxy/pool.h
+++ b/include/haproxy/pool.h
@@ -249,6 +249,19 @@
 	return item;
 }
 
+#else /* CONFIG_HAP_POOLS */
+
+/* no cache pools implementation */
+
+static inline void *pool_get_from_cache(struct pool_head *pool)
+{
+	return NULL;
+}
+
+static inline void pool_put_to_cache(struct pool_head *pool, void *ptr)
+{
+	pool_free_nocache(pool, ptr);
+}
 
 #endif /* CONFIG_HAP_POOLS */
 
@@ -270,10 +283,8 @@
 		return NULL;
 #endif
 
-#ifdef CONFIG_HAP_POOLS
 	if (!p)
 		p = pool_get_from_cache(pool);
-#endif
 	if (!p)
 		p = pool_alloc_nocache(pool);
 
@@ -324,11 +335,7 @@
 		if (unlikely(mem_poison_byte >= 0))
 			memset(ptr, mem_poison_byte, pool->size);
 
-#ifdef CONFIG_HAP_POOLS
 		pool_put_to_cache(pool, ptr);
-#else
-		pool_free_nocache(pool, ptr);
-#endif
 	}
 }