patch 8.1.0487: no menus specifically for the terminal window

Problem:    No menus specifically for the terminal window.
Solution:   Add :tlmenu. (Yee Cheng Chin, closes #3439) Add a menu test.
diff --git a/runtime/delmenu.vim b/runtime/delmenu.vim
index 81df87d..5cefe26 100644
--- a/runtime/delmenu.vim
+++ b/runtime/delmenu.vim
@@ -5,6 +5,7 @@
 " Last Change:	2001 May 27
 
 aunmenu *
+tlunmenu *
 
 silent! unlet did_install_default_menus
 silent! unlet did_install_syntax_menu