Don’t count deprecated constraint statements

Deprecated constraint statements are ignored by the
WikibaseQualityConstraints extension (T180874), so we shouldn’t include
them in the count for a constraint type.

(Also reformats the query to be slightly nicer, and removes an
unnecessary ?itemLabel from the GROUP BY clause.)

Change-Id: I2d43c015e2c0195dc138099d2934b2e9380362fb