The reason to have both export-only XclExpXmlStream
("com.sun.star.comp.oox.ExcelFilterExport") and im-/export oox::xls::ExcelFilter
("com.sun.star.comp.oox.xls.ExcelFilter"), where the latter uses the former to
implement export, appears to be historic.

Get rid of the former service, but keep it as an independent C++ class for now
(still also deriving from XmlFilterBase)---this can likely be cleaned up by
somebdoy versed in those XmlFilterBase details.

With the last use (in oox::xls::ExcelFilter, to instantiate XclExpXmlStream) of
the recently introduced com.sun.star.oox.ExcelFilterExport new-style service
gone now, remove that service again.

Change-Id: Id3adacd293cbe4390242827615f074d4bbe9d85a