Add DeleteChannelD inverse equivalent of RepeatChannelD

[wyli]

In the liver and tumor segmentation model, it's possible to approximate the Brain Segmentation workflow with RepeatChannelD to enable usage of ConvertToMultiChannelBasedOnBratsClassesd. However this results in greater, unnecessary memory usage.

Adding a DeleteChannelD transform would allow the duplicated channels to be pared down before feeding into the network.

[Nic-Ma]

Hi @wyli ,

Thanks for raising this, I think Tam is working on the PR to address it: #1569.

[wyli]

sure, he created this issue originally, I just copied the content here