Remove unused trigger_source parameter in AutofillExternalDelegate

This CL removes unused `trigger_source` parameter in
AutofillExternalDelegate::FillAddressFieldByFieldFillingSuggestion()

BUG=None

Change-Id: I45737907bc8ad6d940c8dbc6d5bfc286e1ecde3c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5414174


Reviewed-by: Jan Keitel <jkeitel@google.com>
Commit-Queue: Peter Kotwicz <pkotwicz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1281969}