bug#70960: Remove mozjs and icu4c versions

[Andreas Enge]

After a recent patch updating the icu4c@68 dependency of 0ad to icu4c,
I have gone through icu4c and mozjs dependents.

It turns out that nothing depends on mozjs@91. Can it be removed?
Then I think that icu4c@69 can also be removed.

The only package depending on mozjs@78 is 0ad. Maybe the dependency
can be upgraded? (Well, we should check this first, upgrading to
mozjs@91 will prevent us from removing this...)

Andreas