Replace pulldata implementation with sugar

[seadowg]

Blocked by #6454

Now that basic CSV secondary instance filters are optimized (by #6454), pulldata can be implemented as syntactic sugar by mapping to this expression:

instance('$instanceId')/root/item[$filterChild='$filterValue'][position() = 1]/$child

There's an example implementation of doing this with a function handler here.

Notes

For this to work, there also needs to be changes in JavaRosa: it should no longer not attach instances if they aren't referenced by an instance expression. Otherwise, instances only referenced with pulldata won't be available to JavaRosa to query.

As part of this, we can also stop creating the specific pulldata DB: it will only be required for forms with search.