remove erroneous extra prototype

git-svn-id: svn://svn.savannah.gnu.org/nano/trunk/nano@2590 35c25a1d-7b9e-4130-9fde-d3aeb78583b8

src/proto.h

@@ -318,9 +318,6 @@ char *histfilename(void);
 void load_history(void);
 bool writehist(FILE *hist, filestruct *histhead);
 void save_history(void);
-#ifndef DISABLE_TABCOMP
-char *get_history_completion(filestruct **h, char *s, size_t len);
-#endif
 #endif
 
 /* Public functions in global.c. */