rm: Remove -i from usage and manpage

We do not support it so do not lie to the user.

rm.c

@@ -5,7 +5,7 @@
 static void
 usage(void)
 {
-	eprintf("usage: %s [-f | -i] [-Rr] file ...\n", argv0);
+	eprintf("usage: %s [-f] [-Rr] file ...\n", argv0);
 }
 
 int
@@ -15,9 +15,6 @@ main(int argc, char *argv[])
 	case 'f':
 		rm_fflag = 1;
 		break;
-	case 'i':
-		rm_fflag = 0;
-		break;
 	case 'R':
 	case 'r':
 		rm_rflag = 1;