Remove water=reservoir from man made structures like water tanks

[AntMadeira]

Hi there.
Recently, it was added to Transifex a preset with emergency=water_tank + natural=water + water=reservoir.
As per wiki definition, a reservoir is an enlarged natural or artificial lake, pond, or impoundment created using a dam to store water.

So, I think 'water=reservoir' should be removed from these kind of presets.
In this case, an emergency water reservoir should be based on the storage_tank, like this:
building=yes
content=water
man_made=storage_tank
+
emergency=water_tank

Regards.