Use java.util.Date instead of java.sql.Date.

java.sql.Date was being used in a context unrelated to SQL and
there's no good reason to use it this way. Note that the claim in
java.sql.Date's javadoc that it normalizes times to day boundaries
is a lie.

Change-Id: Ibb17d3fe22af6c2a41abd51b2158d6af000ecbbf