In Photoshop CC 2019:
- Choose Edit > Presets > Preset Manager.
- From the Preset Type menu choose Brushes.
- Select all the brushes there (click top, then hold Shift and click the bottom).
- Click the Delete button.
- Click the gear icon at top right and choose Restore Default Brushes.
- Click OK, and now you should have only the default folders of brushes.
- Click Done.
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