Rename liftover_complete

From SACGF/variantgrid_private#3761

I misinterpreted what ```liftover_complete``` meant - I thought it meant "liftover succeeded" but it meant "we have stopped trying to liftover"

This has been documented now:

```
:param liftover_complete: Indicates if liftover is complete (and if any missing genome build should be considered an inability to liftover)
builds are newly provided, change etc.
```

But I still think it might be good to rename this for clarity