mergesort: remove llist_mergesort()

Now that all of its callers are gone, remove llist_mergesort().

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

mergesort.h

@@ -1,19 +1,6 @@
 #ifndef MERGESORT_H
 #define MERGESORT_H
 
-/*
- * Sort linked list in place.
- * - get_next_fn() returns the next element given an element of a linked list.
- * - set_next_fn() takes two elements A and B, and makes B the "next" element
- *   of A on the list.
- * - compare_fn() takes two elements A and B, and returns negative, 0, positive
- *   as the same sign as "subtracting" B from A.
- */
-void *llist_mergesort(void *list,
-		      void *(*get_next_fn)(const void *),
-		      void (*set_next_fn)(void *, void *),
-		      int (*compare_fn)(const void *, const void *));
-
 /* Combine two sorted lists.  Take from `list` on equality. */
 #define DEFINE_LIST_MERGE_INTERNAL(name, type)				\
 static type *name##__merge(type *list, type *other,			\