Only define gethookproxy, isinitpath on Session

This fixes an issue where pylint complains about missing implementations
of abstract methods in subclasses of `File` which only override
`collect()` (as they should).

It is also cleaner and makes sense, these methods really don't need to
be overridden.

The previous methods defined directly on `FSCollector` and `Package` are
deprecated, to be removed in pytest 7.

See commits e2934c3f8c and
f10ab021e2 for reference.

src/_pytest/python.py

@@ -52,6 +52,7 @@ from _pytest.config import Config
 from _pytest.config import ExitCode
 from _pytest.config import hookimpl
 from _pytest.config.argparsing import Parser
+from _pytest.deprecated import FSCOLLECTOR_GETHOOKPROXY_ISINITPATH
 from _pytest.deprecated import FUNCARGNAMES
 from _pytest.fixtures import FuncFixtureInfo
 from _pytest.main import Session
@@ -627,10 +628,12 @@ class Package(Module):
             self.addfinalizer(func)
 
     def gethookproxy(self, fspath: py.path.local):
-        return super()._gethookproxy(fspath)
+        warnings.warn(FSCOLLECTOR_GETHOOKPROXY_ISINITPATH, stacklevel=2)
+        return self.session.gethookproxy(fspath)
 
     def isinitpath(self, path: py.path.local) -> bool:
-        return path in self.session._initialpaths
+        warnings.warn(FSCOLLECTOR_GETHOOKPROXY_ISINITPATH, stacklevel=2)
+        return self.session.isinitpath(path)
 
     def collect(self) -> Iterable[Union[nodes.Item, nodes.Collector]]:
         this_path = self.fspath.dirpath()