remove redefinition of legacy extractor base-class

This commit removes the definition of the legacy
extractor base class `BaseMetadataExtractor` from
`datalad_metalad.extractors.base`. It now is imported from
`datalad_deprecated.metadata.extractors.base` and
augmented with a generation-ID.

This should fix mixups with identical class names
from different packages.

datalad_metalad/extract.py

@@ -798,6 +798,8 @@ def legacy_get_file_info(dataset: Dataset,
 
 def legacy_extract_file(ea: ExtractionArguments) -> Iterable[dict]:
 
+    import sys
+    print(repr(ea), file=sys.stderr)
     if issubclass(ea.extractor_class, MetadataExtractor):
 
         # Call metalad legacy extractor with a single status record.

datalad_metalad/extractors/base.py

@@ -22,6 +22,13 @@
 from uuid import UUID
 
 from datalad.distribution.dataset import Dataset
+# XXX this is the legacy-legacy interface, keep around for a bit more and then
+# remove
+from datalad_deprecated.metadata.extractors.base import BaseMetadataExtractor
+
+
+# Add a generation identifier to the old extractor base class
+BaseMetadataExtractor.__generation__ = 2
 
 
 @dataclasses.dataclass
@@ -350,58 +357,3 @@ def get_state(self, dataset):
         object instance is passed via the method's `dataset` argument.
         """
         return {}
-
-
-# XXX this is the legacy-legacy interface, keep around for a bit more and then
-# remove
-class BaseMetadataExtractor:
-
-    __generation__ = 2
-
-    NEEDS_CONTENT = True   # majority of the extractors need data content
-
-    def __init__(self, ds, paths):
-        """
-        Parameters
-        ----------
-        ds : dataset instance
-          Dataset to extract metadata from.
-        paths : list
-          Paths to investigate when extracting content metadata
-        """
-
-        self.ds = ds
-        self.paths = paths
-
-    def get_metadata(self, dataset=True, content=True):
-        """
-        Returns
-        -------
-        dict or None, dict or None
-          Dataset metadata dict, dictionary of filepath regexes with metadata,
-          dicts, each return value could be None if there is no such metadata
-        """
-        # default implementation
-        return \
-            self._get_dataset_metadata() if dataset else None, \
-            ((k, v) for k, v in self._get_content_metadata()) if content else None
-
-    def _get_dataset_metadata(self):
-        """
-        Returns
-        -------
-        dict
-          keys and values are arbitrary
-        """
-        raise NotImplementedError
-
-    def _get_content_metadata(self):
-        """Get ALL metadata for all dataset content.
-
-        Possibly limited to the paths given to the extractor.
-
-        Returns
-        -------
-        generator((location, metadata_dict))
-        """
-        raise NotImplementedError