By Rocky Swift TOKYO, Jan 30 (Reuters) - Japan refrained from intervening in currency markets through last week, official data showed on Friday, confirming that the government's efforts ​to defend the yen have been limited to verbal warnings. Ministry of Finance data showed ‌Japan spent no funds on intervention from December 29 through January 28. On January 23 after a decision by ‌the Bank of Japan, the yen mysteriously jumped 1.7% after trading near an 18-month low against the dollar. The yen rallie ...