metadata: remove Distribution._local

Importing an external module is anti-pattern and very unexpected
behavior. Furthermore, the specific builder implementation we are using
will provision an isolated virtual environmnent and perform the build
there, which is unwanted in various scenarious.

Perhaps there was a time this helper was needed, but we can now
remove this in favor of build.util.project_wheel_metadata[1].

[1] https://github.com/pypa/build/blob/82051d509a87124a46f3766134c11fc8aee9b86a/src/build/util.py#L27

Signed-off-by: Filipe Laíns <lains@riseup.net>

importlib_metadata/__init__.py

@@ -576,18 +576,6 @@ def _discover_resolvers():
         )
         return filter(None, declared)
 
-    @classmethod
-    def _local(cls, root='.'):
-        from pep517 import build, meta
-
-        system = build.compat_system(root)
-        builder = functools.partial(
-            meta.build,
-            source_dir=root,
-            system=system,
-        )
-        return PathDistribution(zipp.Path(meta.build_as_zip(builder)))
-
     @property
     def metadata(self) -> _meta.PackageMetadata:
         """Return the parsed metadata for this Distribution.