You don't have to do this. A single Update, one that goes solely by Feature Type, would adjust all of the improvement-specific ones as well as the generic "remove forest" option. So:
Code:
<GameData>
<BuildFeatures>
<Update>
<Set Production="x"/>
<Where FeatureType="FEATURE_FOREST"/>
</Update>
</BuildFeatures>
</GameData>
If you're worried about this being too open-ended and interfering with some other action that's specific to forests but doesn't chop them, then just change the Where to
<Where FeatureType="FEATURE_FOREST" Remove="true"/>
or something along those lines. Note that placing a lumbermill does not use the BuildFeatures table, so the above change wouldn't interfere with that action.