text: Title: Confusing error message when using `rebot` and output file contains no tests
  Body: To reproduce:
  ```
  $ touch empty.robot
  $ robot --run-empty-suite empty.robot
  ...
  $ rebot output.xml
  [ ERROR ] Suite 'Empty' contains no tests after model modifiers.
  
  Try --help for usage information.
  ```
  Mentioning model modifiers is confusing to users, especially when they didn't use them and probably don't even know what they are. The message is fine if that part is simply removed.
  
  Originally reported and also fixed in PR #5307 by @jnhyperion. A test for the fix needs to be added.