[dvipdfmx] option to suppress the Info dictionary

[Ulrike Fischer]

pdf 2.0 deprecated the /Info dictionary and the accompanying
A-standard, pdf A-4, requires to drop it completly, forcing it to
be empty is not enough. 

Under special conditions the info dictionary is still allowed
but then it should at most contain a /ModDate entry.

Could an option to suppress the entry completly or to restrict it to 
/ModDate be added?

(I tried to suppress entries by setting them to null, which works for 
some of the entries but not for all, e.g. /Producer is filled up with 
the default value by dvipdfmx)

Ulrike