highmem: Remove unused functions

Nothing uses totalhigh_pages_dec() and totalhigh_pages_set().
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: https://lore.kernel.org/r/20201103095856.732891880@linutronix.de

include/linux/highmem.h

@@ -104,21 +104,11 @@ static inline void totalhigh_pages_inc(void)
 	atomic_long_inc(&_totalhigh_pages);
 }
 
-static inline void totalhigh_pages_dec(void)
-{
-	atomic_long_dec(&_totalhigh_pages);
-}
-
 static inline void totalhigh_pages_add(long count)
 {
 	atomic_long_add(count, &_totalhigh_pages);
 }
 
-static inline void totalhigh_pages_set(long val)
-{
-	atomic_long_set(&_totalhigh_pages, val);
-}
-
 void kmap_flush_unused(void);
 
 struct page *kmap_to_page(void *addr);