Composites delete information.

**Current Problem**
Information is unnecessarily deleted by Composites.
In particular the info field of the sampleset can be deleted, despite containing useful information that could be sensibly propagated, such as QPU access time. Note that, if is not sufficient to return info from the bottom level of a Composites hierarchy only, info can be created at many levels.

**Proposed Solution**
https://github.com/dwavesystems/dwave-preprocessing/pull/147 ; for all composites
Maintain the info field of the child solver if its interpretation is unambiguous.

**Alternatives Considered**

**Additional context**
Add any other context here.