scatsat1_l2b and caliop_l2_cloud readers fail to initialise due to failed Dataset import

[ameraner]

Describe the bug
Some readers fail to initialise due to the broken import from satpy.dataset import Dataset (hasn't been around for a long while already).

To Reproduce

import satpy
from satpy.utils import debug_on; debug_on()
readers = satpy.available_readers()

Expected behavior
All readers should initialise fine and appear in the output list.

Actual results
Some readers, particularly scatsat1_l2b and caliop_l2_cloud fail at the Dataset import.

  File "/tcenas/home/andream/code/satpy_latest/satpy/satpy/readers/scatsat1_l2b.py", line 24, in <module>
    from satpy.dataset import Dataset
ImportError: cannot import name 'Dataset' from 'satpy.dataset' (/tcenas/home/andream/code/satpy_latest/satpy/satpy/dataset/__init__.py)

[..]

  File "/tcenas/home/andream/code/satpy_latest/satpy/satpy/readers/caliop_l2_cloud.py", line 28, in <module>
    from satpy.dataset import Dataset
ImportError: cannot import name 'Dataset' from 'satpy.dataset' (/tcenas/home/andream/code/satpy_latest/satpy/satpy/dataset/__init__.py)

[..]

  File "/tcenas/home/andream/code/satpy_latest/satpy/satpy/readers/li_l2.py", line 35, in <module>
    from satpy.dataset import Dataset
ImportError: cannot import name 'Dataset' from 'satpy.dataset' (/tcenas/home/andream/code/satpy_latest/satpy/satpy/dataset/__init__.py)

Note that the li_l2 reader is being removed/rewritten in #2271 .

[djhoese]

I could have sworn there was an issue for these readers, but the bottom line is that these readers are not updated to work with xarray/dask. They are using the Dataset class that existed before we migrated to xarray and dask. So it isn't as simple as a "missing dependency" like some readers might have. These readers are completely defunct and will not work with modern Satpy.

[ameraner]

Ah, in my previous search attempt I didn't find it, but there is an issue already indeed (#1377). So I'll close this, sorry for the noise.