Bug#1099970: libformula: please drop usage of deprecated ant.mk CDBS helper

[Alexandre Detiste]

control: severity -1 serious

Dear Maintainers,

/usr/share/cdbs/1/class/ant.mk removal has now been committed
on CDBS git repository and will be gone from next upload.

libformula is one of the 3 remaining users.

I did my best to migrate all packages team maintained
in "QA Group" and here, but I'm struggling on this one.

Greetings

Alexandre