Remove local declarations of setgrent().

In the nearby future, I'm going to change the prototype of the
setgrent() function. Prevent this port from breaking by removing the
redundant local declarations of the setgrent() function it has.

PR:		211394 (exp-run)
Reviewed by:	antoine
Differential Revision:	https://reviews.freebsd.org/D7364

security/super/files/patch-checks.c

@@ -0,0 +1,26 @@
+--- checks.c
++++ checks.c
+@@ -567,7 +567,6 @@
+ set_u_g()
+ {
+     /* Return 0 on success, -1 on failure */
+-    SETGRENT_T setgrent();
+     void endgrent();
+     int i, j, k = -1;
+     int found_gid = -1, found_egid = -1;
+@@ -1425,7 +1424,6 @@
+ char *grouplabel;	/* name or numeric form */
+ {
+     struct group *gp;
+-    SETGRENT_T setgrent();
+     void endgrent();
+     int numeric_gid;
+     int found_gid, is_numeric=0;
+@@ -1897,7 +1895,6 @@
+     struct group *gp;
+     char **mem;
+     char buf[20];
+-    SETGRENT_T setgrent();
+     void endgrent();
+ 
+     ENTRY item, *found_item;