TileConditions, etc: Make ITileCondToolOfc::getOfcWeights const.

The caching mechanism in TileCondToolOfc is not actually used anywhere, and it spoils the constness of the accessor method. Remove the caching and make the getOfcWeights() method const, changing the interface to take the output object by reference instead of returning it as a pointer. Also remove getNSamples(); it's not used anywhere.

Update clients accordingly.