RT#83284: remove tests for empty elements in MARCXML batch

In the course of working on 83284, I discovered that MARC::File::XML
had a long-standing issue (predating the switch from SAX) where
empty records in an XML batch would not be handled correctly.  The
batch tests slipped into this branch, but I'm moving them to a
different branch.

Signed-off-by: Galen Charlton <gmcharlt@gmail.com>