Remove stale non-static-inline prototype for tree_entry_extract()

When 4651ece8 made the function a "static inline", it should
have removd the stale prototype but everybody missed that.

Thomas Glanzmann noticed this broke compilation with Forte12
compiler on his Sun boxes.

Signed-off-by: Junio C Hamano <junkio@cox.net>

tree-walk.h

@@ -27,7 +27,6 @@ static inline int tree_entry_len(const char *name, const unsigned char *sha1)
 
 void update_tree_entry(struct tree_desc *);
 void init_tree_desc(struct tree_desc *desc, const void *buf, unsigned long size);
-const unsigned char *tree_entry_extract(struct tree_desc *, const char **, unsigned int *);
 
 /* Helper function that does both of the above and returns true for success */
 int tree_entry(struct tree_desc *, struct name_entry *);