tools: Remove unused argument

Since Meson 0.60.0, i18n.merge_file no longer accepts
positional arguments, causing the build to fail with the
message:

"libgda/tools/browser/meson.build:87:5: ERROR: Function does not take positional arguments."
3 jobs for rafaelff-rm-unused-argument in 62 minutes and 1 second (queued for 1 second)
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