EditorPrefs.DeleteAll  

// Clear all the editor prefs keys.
//
// Warning: this will also remove editor preferences as the opened projects, etc

class ClearEditorPrefs extends ScriptableObject {
@MenuItem ("Examples/Clear all Editor Preferences")
static function DoDeselect() {
if(EditorUtility.DisplayDialog("Delete all editor preferences?",
"Are you sure you want to delete all the editor preferences?,
this action cannot be undone.",
"Yes",
"No"))
EditorPrefs.DeleteAll();
}
}