fix: stop seeding a fresh timestamp into translators.json every run

The `sinceLastTag.updated` field was set to `date -u` on every
`scripts/translators.sh --seed` run, but nothing ever reads it. The
release-time credit generator only consumes `.mappings` and
`.sinceLastTag.translators`.

Because the field changed on every run, the seed-translators CI job
produced a diff (and therefore a new Crowdin/seed PR) on every push to
main even when the translator set was unchanged. Drop the field from the
seed write and from the committed JSON so the file only changes when a
contributor actually appears.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RSoN4DDC5F1ehwGeC33652

docs/changelog/translators.json

@@ -75,7 +75,6 @@
   "sinceLastTag": {
     "tag": "v1.12.5",
     "since": "2026-06-19T12:55:37-04:00",
-    "updated": "2026-06-19T17:21:54+00:00",
     "translators": [
       {
         "user": "vitorpamplona",