[Tagging] Removal of rendering for waterway=wadi

[Joseph Eisenberg]

> Intermittent is being used with the key seasonal=*.
> I think you may find the increase in use of intermittent may be from this
> dual tagging.
> I could say tagging for the render.

That's not likely if Openstreetmap-carto is the renderer in question,
because all common values of seasonal=* are treated the same as
intermittent=yes. The SQL is:

"CASE WHEN tags->'intermittent' IN ('yes')
              OR tags->'seasonal' IN ('yes', 'spring', 'summer',
'autumn', 'winter', 'wet_season', 'dry_season')
              THEN 'yes' ELSE 'no' END AS int_intermittent,

(See https://github.com/gravitystorm/openstreetmap-carto/blob/ea73a44105ad1c3a0ebff817d4a8e9ea9233124b/project.mml#L212)

That means that intermittent=yes is currently rendered the same as
seasonal=yes or seasonal=wet_season and so on.

- Joseph