Previously we implemented update as a simple `Delete` + `Insert`
procedure which seemed okay for the moment but it wasn't. `Delete` can
trigger balance and a post balance `seek` which will leave cursor
pointing to an invalid page which `Insert` will try to insert to.
We solve this by removing `Delete` from the execution plan and rely on
`Insert` to properly overwrite the cell where the rowid is the same as
the one we are inserting.
c7e9b3a546