meson: drop unused argument for i18n.merge_file()

Ignored in Meson < 0.60.0, deprecated since 0.60.1 and fatal since 0.61.0.

data/meson.build:34:0: ERROR: Function does not take positional arguments.
data/meson.build:61:0: ERROR: Function does not take positional arguments.
5 jobs for meson-0.61 in 12 minutes and 45 seconds (queued for 2 seconds)