[MorphicUIManager] strange method onEventSensorStartup:

Hello,

I working on the first step of the migration of the UIManager.

```Smalltalk

onEventSensorStartup: anEventSensor

anEventSensor flushAllButDandDEvents

```

the problem is that the only class defining 'flushAllButDandDEvents' method do nothing.

It's normal? what is the responsibility of this method?

Thanks

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