patch 8.1.0500: cleaning up in src/tee may not always work

Problem:    Cleaning up in src/tee may not always work.
Solution:   Use "rm" when appropriate. (Michael Soyka, closes #3571)
diff --git a/src/version.c b/src/version.c
index b1aa8aa..9d700e2 100644
--- a/src/version.c
+++ b/src/version.c
@@ -793,6 +793,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    500,
+/**/
     499,
 /**/
     498,