Remove `StatementContext`

[drebelsky]

With #5094 dropping the prepared statement cache, as far as I can tell, StatementContext no longer serves a benefit over just using a scoi::statement.

[Kanasjnr]

@drebelsky is this issue available to work on? if yes i would love to pick this up

[drebelsky]

@Kanasjnr this issue is available—go for it!