Revert "fix(Man.lua): trigger completion even without arguments" #31572

This reverts commit 7940ec6913.

runtime/lua/man.lua

@@ -576,8 +576,9 @@ function M.man_complete(arg_lead, cmd_line, _)
   end
 
   if #args == 1 then
-    -- XXX: This (full completion) is laggy, but without it tab-complete is broken. #31512
-    return complete('', '', '')
+    -- returning full completion is laggy. Require some arg_lead to complete
+    -- return complete('', '', '')
+    return {}
   end
 
   if arg_lead:match('^[^()]+%([^()]*$') then