Minor improvements to BadZipFile and BadZipfile docs.

I made the doc for the compat alias BadZipfile shorter and used a
directive to document deprecation.

I figured there was no point of talking about zipfile.error (“the old
name” that’s older than the other old name BadZipfile) in the 3.x docs
so I just removed it.

Doc/library/zipfile.rst

@@ -30,15 +30,16 @@ The module defines the following items:
 
 .. exception:: BadZipFile
 
-   The error raised for bad ZIP files (old name: ``zipfile.error``).
+   The error raised for bad ZIP files.
 
    .. versionadded:: 3.2
 
 
 .. exception:: BadZipfile
 
-   This is an alias for :exc:`BadZipFile` that exists for compatibility with
-   Python versions prior to 3.2.  Usage is deprecated.
+   Alias of :exc:`BadZipFile`, for compatibility with older Python versions.
+
+   .. deprecated:: 3.2
 
 
 .. exception:: LargeZipFile