This PR removes an unnecessary check in water.yml.
generated SQL before:
```
SELECT CASE
WHEN waterway='riverbank' THEN 'river'
WHEN "waterway" = 'dock' THEN 'dock'
WHEN "water" = 'river'
OR "waterway" = 'riverbank'
THEN 'river'
WHEN "waterway" = '' THEN 'lake'
ELSE 'lake'
END;
```
generated SQL after:
```
SELECT CASE
WHEN waterway='riverbank' THEN 'river'
WHEN "waterway" = 'dock' THEN 'dock'
WHEN "water" = 'river'
OR "waterway" = 'riverbank'
THEN 'river'
ELSE 'lake'
END;
```
The `waterway=''` test is purely redundant because it returns the same value as the fall-through ELSE case: `lake`.
df6906b7b5