Misleading warning message in decollate=False

[Nic-Ma]

Is your feature request related to a problem? Please describe.
Issue reported from NVIDIA QA team today:

Got this warning message in the Pathology program:
MONAI transforms expect `channel-first` data, `decollate=False` may not work here.
It has started since MONAI v0.6, where the default has changed to decollate=true.
@Nic-Ma isn’t this warning a bit misleading? Obviously, here everything is working and data is channel first but we need to have “decollate=false” for prob map generation.

if postprocessing is not None:
    if not decollate and isinstance(postprocessing, Transform):
        warnings.warn("MONAI transforms expect `channel-first` data, `decollate=False` may not work here.")

[Nic-Ma]

Hi @wyli @ericspod @rijobro ,

If you guys don't have concerns, I plan to change this warning to debug level message.

Thanks in advance.

[rijobro]

Certainly shouldn't be a warning. If it's just a note on usage then it should be in a docstring somewhere.