Drop create_extract_refresh_subscription sample, defer to #1861

samples/create_extract_refresh_subscription.py depends on
SubscriptionItem.on_extract_refresh(), which is added by #1861 and
was already removed from this PR's diff along with the rest of the
refreshExtractTriggered work. #1861's branch already carries the
same sample byte-identical.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: jacalata