SqliteDb.scala: remove SqlInt type (breaks legacy compatibility)

The SqlInt type was unnecessary and made it difficult to do pattern
matching on the results of queries because you had to handle both
SqlLong and SqlInt. For example, before you would have had to write
code like:

db.foreachRow("SELECT x FROM foo") {
  case Seq(SqlInt(x)) => println(x)
  case Seq(SqlLong(x)) => println(x)
}

to take advantage of case class extractors.

Now you can do:
db.foreahRow("SELECT * FROM foo") { case Seq(SqlLong(x)) => println(x) }

This change breaks compatibility with an legacy code that uses SqlInt.