Undo some expansion of "reference" parameter

This keeps most of the changes from the previous commit, but it
undoes the expansion of the git object types a lightweight tag can
refer to into GitPython git.objects.base.Object-based types, which
seems more misleading than helpful because an uncareful reading
could lead to an incorrect belief that the corresponding argument
should or could be an object of such types.

git/refs/tag.py

@@ -106,8 +106,7 @@ def create(
 
         :param reference:
             A reference to the :class:`~git.objects.base.Object` you want to tag.
-            The referenced object can be a :class:`~git.objects.commit.Commit`,
-            :class:`~git.objects.tree.Tree`, or :class:`~git.objects.blob.Blob`.
+            The referenced object can be a commit, tree, or blob.
 
         :param logmsg:
             If not None, the message will be used in your tag object. This will also