Stray theming files in app data #34606

Steps

1. Setup 24.0.6
2. Set an admin theme
3. Upgrade to 25.0.0
4. Change the theme again
5. Check the appdata*/theming folder using the "tree" command

Expected result

No numeric folders under "appdata*/theming" any more.

Actual result

While the theming cache stuff has moved to "appdata*/theming/global", the old ones are still there.

Task

• write a repair step that will run one time to delete all folders in "appdata*/theming" except "global" and "users".

@Pytal @skjnldsv follow up of #34599