remove unused columns in list of LibreOffice ODF Extensions

[Regina Henschel]

Hi all,

the table in 
https://wiki.documentfoundation.org/Development/ODF_Implementer_Notes/List_of_LibreOffice_ODF_Extensions
has the columns 'ODF Version(s) Extended' and 'False Positive Validation 
Errors'. These columns have no entries. Because the table is already 
very wide, I'm going to remove these two columns.

Any objections?

Kind regards
Regina