Fix geneformer notebook tests by removing 10m_bnmo2 model (#649)

There seems to be an issue with the `geneformer_10m_bnmo2` checkpoint
trying to load a no-longer-existent `BERTMLMLossWithReductionNoForward`
layer. Commenting out this model from the celltype classification
notebook until we can fix it.

Signed-off-by: Peter St. John <[email protected]>