How do I remove radio from sandisk clip sport plus

You cannot remove the radio from the device, however you can remove it from the Main Menu by going into Settings > System Settings &:

1. Select Customize.
2. Select the name of the feature you want removed.
3. Press the Select button to toggle between On or Off.
4. Press the Back button to return to previous menu.

This is described on pg. 34 of the manual.

Will there ever be a firmware without radio like the sansa clip plus?

not for the new players. The menu has an option to remove the different menu options. 

Y not the old players you are able to for example the sansa clip plus?

I’m not sure I really understand your questions but the older player did not have the option to remove menu options. the new ones do so there is no special FW to remove a specific option.