Remove deprecated positional arguments for translation merges

[fossfreedom]

Meson has now removed the positional arguments for
the translation merges. This causes a FTBFS scenario.

[travrei]

Nice! Now i can use it!

[eli-schwartz]

Meson has now removed the positional arguments for the translation merges. This causes a FTBFS scenario.

This description gives an inaccurate impression that Meson dropped support for something which it formerly supported.

This is incorrect. Meson never supported a positional argument here at all, and never did anything with it if you added one anyway. During routine refactoring, type validation was added to this function to make sure that any kwargs use the values that are documented to work -- in the process, it also validated that, per the documentation, no positional arguments are used.

Naturally, this broke any meson.build which contained an invalid positional argument, which turned out to be... lots of projects.