mm/page_alloc: fix build with CONFIG_UNACCEPTED_MEMORY=n

When has_unaccepted_memory() is unused, it prevents kernel builds
with clang, `make W=1` and CONFIG_WERROR=y:

mm/page_alloc.c:7036:20: error: unused function 'has_unaccepted_memory' [-Werror,-Wunused-function]
7036 | static inline bool has_unaccepted_memory(void)
|                    ^~~~~~~~~~~~~~~~~~~~~

Fix it by removeing the CONFIG_UNACCEPTED_MEMORY=n stub.

Link: https://lkml.kernel.org/r/20240905142220.49d93337a0abce5690e515d9@linux-foundation.org
Reported-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Closes: https://lkml.kernel.org/r/20240905171553.275054-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/page_alloc.c

@@ -287,7 +287,6 @@ EXPORT_SYMBOL(nr_online_nodes);
 
 static bool page_contains_unaccepted(struct page *page, unsigned int order);
 static bool cond_accept_memory(struct zone *zone, unsigned int order);
-static inline bool has_unaccepted_memory(void);
 static bool __free_unaccepted(struct page *page);
 
 int page_group_by_mobility_disabled __read_mostly;
@@ -7061,6 +7060,11 @@ static bool try_to_accept_memory_one(struct zone *zone)
 	return true;
 }
 
+static inline bool has_unaccepted_memory(void)
+{
+	return static_branch_unlikely(&zones_with_unaccepted_pages);
+}
+
 static bool cond_accept_memory(struct zone *zone, unsigned int order)
 {
 	long to_accept;
@@ -7088,11 +7092,6 @@ static bool cond_accept_memory(struct zone *zone, unsigned int order)
 	return ret;
 }
 
-static inline bool has_unaccepted_memory(void)
-{
-	return static_branch_unlikely(&zones_with_unaccepted_pages);
-}
-
 static bool __free_unaccepted(struct page *page)
 {
 	struct zone *zone = page_zone(page);
@@ -7128,11 +7127,6 @@ static bool cond_accept_memory(struct zone *zone, unsigned int order)
 	return false;
 }
 
-static inline bool has_unaccepted_memory(void)
-{
-	return false;
-}
-
 static bool __free_unaccepted(struct page *page)
 {
 	BUILD_BUG();