rev(1): drop "rpath" promise in no-file branch

[Scott Cheloha]

We don't need "rpath" if we're only processing the standard input.

ok?

Index: rev.c
===================================================================
RCS file: /cvs/src/usr.bin/rev/rev.c,v
retrieving revision 1.15
diff -u -p -r1.15 rev.c
--- rev.c       29 Jan 2022 00:11:54 -0000      1.15
+++ rev.c       8 Feb 2022 16:38:46 -0000
@@ -68,6 +68,9 @@ main(int argc, char *argv[])
 
        rval = 0;
        if (argc == 0) {
+               if (pledge("stdio", NULL) == -1)
+                       err(1, "pledge");
+
                rval = rev_file(NULL);
        } else {
                for (; *argv != NULL; argv++)