Querier is passed to Migrate by reference

[milapsheth]

A reference to the querier is passed to Migrate (&querier) as opposed to other wasmVM methods like Execute that receive querier as-is. Both Execute and Migrate expect the same querier type in their interface declaration.

Is there a reason for this discrepancy?

[chipshort]

I'm pretty sure there is no reason for this. Both passing by reference or by value work equally well in this case.