uniq: Fixup program usage and manpage

Remove -i as it is not required by POSIX.  We'll add it if we
hit scripts that require it.

uniq.c

@@ -25,7 +25,7 @@ static long prevlinecount = 0;
 static void
 usage(void)
 {
-	eprintf("usage: %s [-cdiu] [input]]\n", argv0);
+	eprintf("usage: %s [-cdufs] [file]\n", argv0);
 }
 
 int
@@ -34,8 +34,6 @@ main(int argc, char *argv[])
 	FILE *fp;
 
 	ARGBEGIN {
-	case 'i':
-		eprintf("not implemented\n");
 	case 'c':
 		countfmt = "%7ld ";
 		break;