shadow.h: remove declaration of function not implemented

Author: richfelker

include/shadow.h

@@ -28,7 +28,6 @@ void setspent(void);
 void endspent(void);
 struct spwd *getspent(void);
 struct spwd *fgetspent(FILE *);
-struct spwd *sgetspent(const char *);
 int putspent(const struct spwd *, FILE *);
 
 struct spwd *getspnam(const char *);