clean up RtfExport::WriteInfo()

The \vern output was never parsed, and Word uses the generator field, so
let us do the same. And with the standard generator string, if we ever
need to parse it, we already have a parser for it in the ODF filter.

Change-Id: I57f25a6414b2b753a23cf82b691e364d84e4bb44
fdo#76101 move testcase to CppunitTest_sw_ooxmlsdrexport

The motivation is that this test takes time to execute (and we're
testing a limit here, so it's not easy to speed it up), though moving it
out of CppunitTest_sw_ooxmlexport is still possible (which is the
current critical path during a toplevel 'make').

Change-Id: Ibe6580f8aea1439f4feb281996f2f4bbd46ff4ce
coverity#735895 Unchecked dynamic_cast

Change-Id: I6c2cc90668a2158a0b5bf638ce520c8af7731f4e