[lmi] Can we remove unused elements of the columns title map?

[Vadim Zeitlin]

 Hello,

 AFAICS, we currently have a lot of unused elements in the "title_map"
defined in Ledger::write(xml::element&) function in ledger_xml_io.cpp
because many of the columns for which titles are defined in this map do
not, in fact, correspond to any element of mcenum_report_column and hence
can't appear in any supplemental report.

 I'd like to remove these unused titles because I plan to change the format
of all of them: it doesn't make sense to keep using the hack with
underscores which (in conjunction with the recursive "text-word-wrap"
function in fo_common.xsl which is almost as easy to understand as
Ackermann function), was used to break the titles into lines when we can
simply use "\n" characters in them now. And, of course, being lazy, I'd
like to update only half of the strings that are actually used, rather than
all of them.

 Would anything be lost if I removed them? Or would it be easier for you if
I preserved them for now? Please notice that I don't think that it's going
to make reviewing the changes any easier because all these unused titles
would still need to be changed, instead of being removed.

 Of course, if there are any plans to actually extend mcenum_report_column
to include all the columns for which titles are defined even though they
don't appear in any supplemental reports, it would be better to keep them.
This could also make sense if you plan to make any other, more sweeping,
changes to this area in near future as handling of these column titles,
with different definitions here, in ledger_metadata_map() in
ledger_text_formats.cpp and the names defined by the enum itself, with a
"TODO" comment saying that they should be made "nicer-looking", is
definitely not ideal and could be improved.

 Final possibility would be to keep all this code completely unchanged
and create _another_ set of column titles in the PDF generation code
itself. This would make the upcoming review simpler, and would allow me to
reuse the same map for all columns used in the illustration tables, whether
they correspond to mcenum_report_column elements or not. But it would also
mean that the columns appearing both in "normal" and "supplemental" reports
would use the same name in both, which actually seems like an advantage to
me but which is _not_ the case currently. E.g. consider a basic column such
as "AcctVal_Guaranteed" which uses "Account Value" labels in all the
different tables it appears in, but "Guar Account Value" in supplemental
reports. So I'm not really sure whether it would be a good idea.

 Please let me know if you have any thoughts/advice, thanks in advance!
VZ