Adapt method for remote reading

[gerritholl]

Currently sattools uses the branch from pytroll/satpy#1321 to implement remote reading and passes the file_system keyword argument down to the ABI reader. This is unlikely to be what will be implemented in Satpy. It's already superseded by the superior pytroll/satpy#1439 but discussions on a pathlib implementation within fsspec are ongoing (see drivendataorg/cloudpathlib#96 and fsspec/filesystem_spec#434). sattools should follow what happens there closely and then adapt its implementation.